MOLECULAR GASTRONOMY: Part III - Investigations and Models (To be continued)

PART THREE:  INVESTIGATIONS AND MODELS

In part 3, Investigations and Models, the author presents a collection of chapters that address ways to improve upon specific methods of preparing and cooking food in terms of flavor, aroma, and texture.  The author delves primarily into how structure and chemical properties play a role in the transformation of food stuff by heat, i.e. cooking.  For example, the author looks at the structural and chemical changes taking place in the cooking of meat to understand the best method for preserving tenderness for different cuts of meat.  He also looks at the chemical basis for the aroma, taste, flavor, texture, and color that result in the preparation of different foods: sausages, bread, pasta, trout, eggs, meat, Spanish hams, etc.  Many of the research mentioned involved both standard chemical analysis using gas chromatography and mass spectrometry and also human sensory tests done by qualified testers.  The Maillard reactions, a well-known type of organic reaction, were mentioned many times attributing to it the aroma and color of bread crusts, roasted coffee, roasted meats etc.  The role of phospholipids in changing the aroma of roasted meat was attributed to its structural feature of having both hydrophilic and hydrophobic parts.  GC-MS was used to determine that there are about 100 organic compounds responsible for the taste and aroma of hard sausages.  Knowledge of the type of odorant and favor molecules also allow cooks to devise ways to have more control over how these molecules are released either during the cooking or the eating process.  More detailed examples are outlined in my chapter notes given in the appendix.

THE SECRET OF BREAD:

·         The two main components of wheat flour are starch granules which swell up with water and proteins which form a glutinous network as dough is needed.

·         These proteins are called gluten and they form a “viscoelastic network of proteins that becomes elongated by pulling and then partially reverts to its initial form when the tension is relaxed”.

·         Specifically, this glutinous network of dough is made up of prolamins which are water insoluble wheat proteins.  There are two types of prolamins:  gliadins (one single protein chain) and glutenins (composed of several protein chains held together by two covalently bonded sulfur atoms).

·         Glutenins have a central domain containing 440-680 amino acids formed of short repeated sequences and flanked by two terminal domains containing cysteines.

·         In 1998, it was found that chains of prolamins bond together through dityrosine bonds which increased during kneading.  Two types of dityrosine bonds form: dityrosine (two benzene groups are linked by the C atom of the –OH group) and isodityrosine (the two benzene groups are linked by an oxygen atom on one –OH group bonding to the C atom in the –OH group in the other tyrosine).

·         The presence of peroxidase in bread has also been correlated with the formation of these dityrosine bonds.

·         Oxidizing compounds like ascorbic acid and potassium bromated also increase the number of dityrosine bonds.

·         The author notes that perhaps the amount of dityrosine bonding between prolamine chains can be used as a measure of the quality of gluten and the dough.

YEAST AND BREAD

·         “Bread owes its flavor to fermentation.”

·         The flavor of bread comes from the fermentation products of saccharomyces cerevisiae.

·         There are three different methods of making bread with or without yeast and with or without fermentation.

·         Direct yeast fermentation – (most common) dough composed of flour, water, yeast, and salt is kneaded for 20 minutes, allowed to ferment for 45 minutes, then divided into lumps, fermented again for another 1 hour and 40 minutes and then baked at 250 C for 30 minutes.

·         Sponge method – same as the first method above except the dough is pre-fermented in a semi-liquid state (water is combined with a smaller quantity of the flour and allowed to ferment for several hours before the rest of the flour is added to turn it into a dough with the right consistency for bread-making).

·         Sourdough method – a starter (sourdough) is created by cultivating beforehand a natural microflora composed of yeast and lactic bacteria; this starter is then used to start the fermentation process in the bread dough.

·         Sponge method yields twice and the sourdough method yields 20 times the acetic acid obtained by direct fermentation.  The sourdough method also produces lactic acid.

·         Fermenting dough using yeast produces 3-hydroxy-2-butanone, 3-methyl-1-butanol, and 2-phenylethanol (gives the odor of wilted rose).

·         Without yeast, ordinary bread is more abundant in monounsaturated and polyunsaturated aldehydes and alcohols such as pentanol and benzyl alcohol, probably resulting from the oxidation of lipids in flour.

·         To study the chemical transformations in bread dough, scientists also looked at uncooked dough under various conditions and carried out chemical analysis through solvent extraction and chromatography and also human detection of smells.  They found that:

o   There was a general increase in different alcohols, ketones, esters, and lactones but a decrease in aldehydes.

o   With yeasts, more alcohols are formed.

o   With longer and faster kneading by mechanical means, flours produce hexanol which gives a stale, oily smell.

CURIOUS YELLOW

·         An egg yolk consists of concentric layers of varying shades of yellow because of the variation in the amount of yellow pigment produced during the day and during the night based on the “rhythm of feeding” by the hen.

·         Yolk is a mixture of granules suspended in a “plasma” phase.  It is about half water, a third lipids, and 15% proteins [by mass or volume?]. 

·         The granules are composed of low-density lipoproteins and high-density lipoproteins.  The LDL’s form a gel at about 70 C and cause the yolk to set during cooking.

·         Yolks are used in making mayonnaise and in this process the emulsion quality is important.  Some  the factors affecting the emulsion quality observed are below:

o   The plasma proteins are completely water soluble at all pH’s and salt concentrations.  The granules have low solubility at pH 3 but becomes more soluble as the pH goes to neutral in a low-salt solution (“sodium ions replace calcium ions, which establishes bridges between the granular proteins inside the granules, with the result that these proteins are released”).

o   The solubility properties are important in the emulsification process.  The other factor is the movement of oil droplets in water; less movement creates a more stable emulsion.  At pH 3, there is minimal movement in the plasma (salt concentration has no effect).  The emulsions from granules are affected by the acidity and the salt concentration.

o   Proteins are better at preventing any upward movement by oil droplets than do the phospholipids.

GUSTATORY PARADOXES

·         “The environment of aromas affects our perception of them.”

·         The taste of vinegar is modified when a lot of sugar is added to it even though its pH is unchanged.  This is because, as addressed in an earlier chapter, our perception of one type of taste may be enhanced or diminished by the presence of another taste.

·         The same type of interaction and effect on each other takes place in olfactory receptors.

·         When food is placed in the mouth, the water-soluble taste molecules first have to diffuse through saliva before reaching the taste receptors.  Odorant molecules first have to vaporize to make their way toward the nasal olfactory receptors.  Their variation in solubility in water results in an uneven distribution inside the mouth and its cavities.  Thus the study of aromas of food necessarily involves knowledge of the movement of molecules between liquid (polar and nonpolar) and gaseous phases.

·         To study these factors, one experimental set-up involved measurements of the distribution molecules in the various phases that exist in an oil-water mixture (water, oil, air above water, air above oil). 

·         One finding is that, when the molecules are first dissolved in the oil, their vapor move to the air above the oil, diffuse through the water, and then move to the air above the water [not perfectly clear about this description by the author].

·         Also, they observed that “transfer was more rapid from oil to water than from water to oil in the case of the esters and ketones but more rapid from water to oil than from oil to water in the case of alcohols and aldehydes”.  This was a surprising result as alcohols, for instance, are water-soluble.

·         Odorant molecules must first penetrate the mucus layer before arriving at the olfactory receptors and become dissolved in the hydrophobic phase of the cell membrane.

·         When human noses were used to detect the aromas, there was a difference from those detected by the non-human detectors in the case of 1-octane-3-ol (mossy smell), benzaldehyde (almond smell), and acetophenone (beeswax smell).  There was no difference however with linalool (gives the odor of lavender and bergamot)

·         “The presence of water vapor can affect the perception of an aroma.”

THE TASTE OF FOOD

·         “The texture of vinaigrettes determines their odor.”

·         Odorant and taste molecules can bind to odorless starch and proteins.  Adding too much flour to sauces can make it tasteless.

·         “In homogenous phases such as solutions, the release of odorant molecules depends on the viscosity of the system.”

·         Foods are dispersed systems:  foams (air bubbles trapped in solids or liquids), emulsions (oil droplets dispersed in water), and suspensions (solids in liquids).  Odorant and taste molecules must escape both the dispersed particles and the “solubilizing” medium.

·         A study was done by two agronomical and nutrition institutes in Dijon to investigate how odorant molecules are released.  They studies vinegar-based sauces.

·         Composition of vinegar-based sauces:  the aqueous phase consists of wine vinegar, lemon juice, and salt, sunflower oil emulsified with the help of whey proteins, and a mixture of xanthan (a polymer obtained by microbial fermentation of glucose) and starch to stabilize the sauce.  Odorant molecules were added:  isothiocyanate in the oil phase (hint of mustard) and phenyl-2-ethanol and ethyl hexanoate (rose and fruity notes).

·         “Although the acid taste was preponderant, the tasters struggled to describe the other sensations.”  However, some observations: the overall odor, the taste and odor of the egg, the mustard odor, and the butter taste increased but the citrus odor decreased as the size of oil droplets increased.

·         Results of analysis of volatile molecules in the air above the sauces:  lower concentrations of water-soluble components detected as the oil droplet size decreased and more abundant oil-soluble molecules.

LUMPS AND STRINGS

·         Flour is made up mostly of starch.  There are two types of polymers in starch, linear amylase and branched amylopectin.  Amylose is soluble in hot water while amylopectin is not.  When hot water is added to flour, the amylase dissolves while water permeates within the amylopectin molecules causing granules that swell up and form a gel (starch paste).  This gel slows down and even stops the diffusion of water into the center of the granules and lumps are formed.

·         Pre-soaking gelatin helps the separation and pre-dissolving of protein layers which prevents the formation of strings (bound protein polymers that water cannot penetrate through) when making gelatin.

FOAMS

·         “The stability of foams depends on the arrangement of the proteins at the interface between the water and air.”

·         The stability of foam depends on the formation of small enough bubbles so that the surface tension is stronger than gravitational forces which cause the air to rise and the water to fall.  To stabilize foam, the viscosity of the liquid phase should be increased and the absorbent films should have good drainage properties.  In protein foams, the film’s integrity and strength are affected by intramolecular and intermolecular forces between and within protein molecules.  This complex network of interactions makes it difficult to study the effects of proteins on foam stability.  They found, however, that the concentration of soluble proteins does not have much an effect.  Insoluble proteins that fold in complex ways are hard to study.  Nevertheless, they observed that for globular and nonglobular proteins, interfacial tension increases with the concentration of the foam proteins.

HARD SAUSAGE

·         In this chapter, the author looks at characterizing the molecular composition of sausage to understand their aromatic qualities.

·         Using GC-MS, scientists detected about 100 organic compounds produced by enzymes and fermentation agents in meat.

·         It was determined that the flora used to age sausages play a big role in producing aromas.

·         In an experiment, 6 mixtures of acidifying and aromatizing bacteria were used in preparing 30 sausages (5 samples each mixture).  Some findings (the aroma was determined by trained testers based in some agreed to terms for describing aromatic properties):

·         Oxidation of lipids played a “preponderant role in determining aromatic qualities”:

o   Rancid smell is correlated with aldehydes, alkanes, and alcohols

o   Good sausage smell is correlated with methyl ketones and methyl aldehydes

o   Degradation of sugars “favors the development of vinegar odors produced by acetic acid or of butter aromas produced by 2,3-butanediol”.

·         Conclusion: aromatic quality of sausages depends on the quality of the strains used in the maturation process.

·         Other factors that affect the aromatic quality are length of the curing process and the type of packaging.  Drying loses some of the aroma because some of the volatile organic compounds evaporate with the water but it also concentrates the salts which bring out the flavor.

·         In studies of the mechanisms of aromatization, they found traces of pepper (terpenes), garlic (sulfur-containing molecules), and brandy (esters formed by the reaction of ethyl alcohol with fatty acids produced by salting).

SPANISH HAMS

·         Since 1970’s, it’s been known that the aroma of certain foods like cheese is due to degradation products of proteins and lipids. 

·         In the 1990’s, similar analysis was done and similar findings resulted when the transformation of proteins and lipids at every curing step for ham was studied.  They found two types of reactions responsible for producing the molecules of aroma:

o   Maillard reactions between amino acids and sugars during prolonged storage periods which cause darkening

o   Strecker degradations which are reactions between amino acids and acids like fatty acids from lipid degradation.  These produced aldehydes that contribute to the aroma.

§  The aldehydes play a role in the Maillard reaction forming products that slow down the process by which fats turn rancid.

·         Analysis of the volatile molecules from Spanish hams, Spanish chemists found:

o   both linear alkanes from the decomposition of lipids and ramified (branched) alkanes “a consequence of the distinctive acorn-based diet on which Iberian pigs feed”.

o   Linear aldehydes produced by Strecker reactions and reactions associated with unsaturated fatty acids turning rancid

FOIE GRAS

·         “It melts less and tastes better when it is cooked immediately after the geese are slaughtered.”

·         Did not care much for this chapter.

ANTIOXIDANT AGENTS

·         The autoxidation of fatty acids is responsible for fats turning acid upon contact with air. The steps involved are:

o   Light breaks the –C-H bonds of a lipid

o   Unstable –C free radicals are formed

o   The C radicals react with oxygen in the air to form –COO free radicals

o   The –COO radicals react with other –C-H to create a new –C radical that propagates oxidation

·         Steps to slow down and minimize this chain reaction are protecting the food from oxygen in the air and light and using antioxidants (substances that inhibit oxidation).

·         Some naturally occurring antioxidants found in food are tocopherols (vitamin E) in virgin oil and ascorbic acid (vitamin C) in lemon.

·         The food processing industry uses phenols as antioxidants.  Phenols and their esters (aromatic in its chemical nature and stable) because of their aromaticity (renders stability) are able to inhibit or slow down oxidation because when they react with a radical and lose an electron and become radical themselves, the delocalized nature of the unpaired electron creates less reactive radicals.  Thus, the radical reaction is not propagated at the same rate to sustain a chain reaction.

·         In the 1990’s, scientists came up with a way to test the antioxidant properties of some compounds.  In this test, oxygen is bubbled into dodecane, a lipophilic solvent.  Both the fat and the antioxidant compound to be tested are then dissolved in the dodecane at 110 C.  In a specific test using gas chromatography, they determined that it takes 3 hours for half of the methyl linoleate (test fat) to be oxidized. They then test the antioxidant “power” of other compounds by measuring how much the oxidation half-life of methyl linoleate is reduced or increased.

·         Using this test, they were able to compare the antioxidant power of plant phenol acids with 4 antioxidants commonly used in the food processing industry:  butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), 2-tertbutylhydroquinone (TBHQ), and propyl gallate.  In general, they found that the antioxidant ability of a compound is correlated with the number of hydroxyl groups around the benzene ring and the degree of stabilization by delocalization of electrons.

·         Various extracts from plants were tested and they confirmed the presence of antioxidant compounds in rosemary, sage, cloves, and ginger.  Sage, in particular, was found to contain 6 powerful antioxidant compounds: carnasol, carnosic acid, and isorosmanol in large quantities and also rosmadial, rosmanol, and epirosmanol.

TROUT

·         Filet of fario trout contains 65-70% water, 20-24% proteins, and 2-12% lipids [by mass, I am guessing].

·         The pink color of filets are due to carotenoid molecules (astaxanthin and canthaxanthin).  The color of the fish does not seem to be a good indicator of the quality of its filet because the color is mostly due to the fish’s diet.

·         Fish meat has a different protein structure from that of other animal meat.  Animal muscle usually is composed of long fibers wrapped with collagen and collected in bundles which are also sheathed in collagen.  “The cooking of meat therefore involves a delicate compromise between hardening, which results from the coagulation of the proteins contained in these cells, and tenderizing, a consequence of separation and dissociation of the collagen molecules”.  Fish meat contains a small amount of collagen and their muscle fibers are arranged in sheets with only the surface protected by collagen.  Lipids located within the muscle sheets keep the sheets together and determine the texture of the flesh.  Trout flesh is known to be firmer than other freshwater fish like carp and catfish.

·         Heating (in the process of cooking) causes the muscle proteins to coagulate increasing the mechanical resistance of the muscle fibers.

COOKING TIMES

·         Because cooking is “fundamentally a transformation of foods by heat”, the amount of tenderness and juiciness in cooked meat depend on the amount of cooking time.

·         Media for heating include gases, liquids, solids, and waves.

·         Cooking by gas includes smoking, drying, braising, steaming, and oven roasting.

o   In smoking and drying, cooking is slow because the temperature of the heated air is not much above the room temperature.

o   Cooking by steaming is faster because the food receives both the kinetic energy of the steam and the energy released by condensation.

o   In oven cooking, the air can be heated to much higher temperatures.

·         How much time to cook?  Meat twice as thick takes 4 times the cooking because both the distance the heat travels and the quantity of meat to be heated are doubled.  “For a spherical body, the cooking times is proportional to the mass raised to the power of two-thirds, a relationship described by a curve that flattens out after an initially rapid rise.”

·         The chemical transformations taking place in the braising method of cooking are:

·         “…At 40°C (104° F) meat becomes opaque because the proteins in it, initially folded into a ball, begin to unfold before they coagulate (thus becoming denatured); at 50°C (122°F) the muscle fibers begin to contract; at 55°C (131°F) the fibrillar part of myosin (a protein that, along with actin, is essential for muscle contraction) coagulates, and collagen (a protein that gives meats their toughness) begins to dissolve; at 66°C (151°F) various other proteins coagulate; at 70°C (158°F) myoglobin no longer fixes oxygen, causing the inside of meat to turn pink; at 79°C (174°F) actin coagulates; at 80°C (176°F) the cell walls are ruptured and the meat becomes gray; at 100°C (212°F) water evaporates; and at temperatures higher than 150°C (302°F) so-called Maillard (and other) reactions produce brown and flavorful results.”

THE FLAVOR OF ROASTED MEATS

·         Fats are found to participate in Maillard reactions that produce compounds that make up the “chief aromatic components of heated foods”.

·         Maillard reactions occur between sugars and amino acids from proteins.  They produce compounds that give favor to bread crust, roasted aroma of meats, beer, and chocolate and form melanoidins which give food a characteristic brown color.

·         In addition to Maillard reactants, chemists have found that phosphate sugars, nucleotides, peptides, glycopeptides and organic acids are also precursors of volatile compounds in cooked meats.

·         ROLE OF PHOSPHOLIPIDS:  Earlier studies showed that removing triglycerides from meats did not alter its odor after cooking but removing phospholipids did to one of roasted meat and biscuit.

·         Phospholipids contain polyunsaturated fatty acid residues that can undergo oxidation and they also contain a molecular portion soluble in water which can react with oxygen also.

·         To study the role of phospholipids in the Maillard reactions, scientists set-up a simple reaction in which cysteine (sulfur-containing amino acid chosen because it contains sulfur which is involved in the production of cooked meat aroma) is reacted with ribose (“a sugar known for its activity in cooking that can be released in nucleotides [?]).  They then added either fatty acids found in phospholipids (linoleic acid, palmitic acid, and ethanolamine) or the principal phospholipids in meats (phosphatidylcholine and phosphatidylethanolamine) and the mixtures were heated to 140 C.

·         They used gas chromatography to study the product profiles focusing on heterocyclic compounds (with meaty taste) and products of lipid oxidation.

·         Findings:

o   Phospholipids play a greater role in producing the aroma of cooked meats and these aromas come from two effects:

§  Carbonylated compounds which create a fatty aroma (from the oxidation of fatty acids)

§  Interaction of lipids and their degradation products with the direct and intermediate products of Maillard reactions

·         “Further analysis showed that the odors of the modeled systems resulted more from a disturbance of Maillard reactions than from lipid oxidation.  Although lipids do not come into contact with compounds dissolved in the aqueous phase, phospholipids, because of their polar head, are partially soluble and can react with the intermediate products of Maillard reactions.”

TENDERIZING MEATS

·         In this chapter, the author looks at the best method for cooking a cut of meat from a structural viewpoint to preserve tenderness.

·         The response of different types of muscle myofibrils to heat and proteolytic enzyme and the quantity of collagen determine the amount of time needed to “age” meat and the cooking method to optimize tenderness.

AL DENTE

·         In this chapter, the author discusses the structure and the transformations taking place in pasta in the cooking process to explain how pasta can be cooked with just the right amount of firmness and without sticking together.

·         Fresh pasta can be made by mixing flour (usually wheat), a bit of salt, water, oil, and eggs and kneading. 

·         In the cooking process, the starch from the flour absorbs water and expands.  The proteins in the egg and flour form an insoluble network that binds the starch granules tightly together which prevents their being dissolved into the cooking water.

·         To ensure that the pasta cooks to the right firmness and does not stick together, the protein network must form before the starch granules swell up.  If not, the amylose dissolves in the water and the amylopectin starts to coat the outside which causes the pasta to stick to each other.  The author then suggests the following to ensure firm pasta that do not stick together:

·         The protein content must be substantial to provide the correct proportion needed for binding the starch granules.  The author suggests using hard wheat as it has a good amount of gluten. If not, eggs must be added. 

·         Kneading the dough enough and adding enough water to hydrate molecules are required to ensure that the proteins are hydrated enough to bind together.

·         Adding the pasta to boiling water reduces the amount of cooking time needed and also ensures reducing the loss of starch [presumably to encourage substantial protein network build up to bind the starch granules].

·         Cooking the pasta in acidic water (about ph 6, by addition either of vinegar or lemon juice) facilitate protein network formation because “proteins in water with a pH of 6 have an electrically neutral form, allowing them to combine more easily and form a network that efficiently traps the starch”.

FORGOTTEN VEGETABLES

·         In this chapter, the author discusses enlivened interest in using “forgotten vegetables” in contemporary dishes and summarizes some of the challenges faced by growers to promote demand for them.  At the time of writing, the author mentions Japanese artichokes, pepinos, Cape gooseberries, Peruvian parsnips, tuberous chervil, sea kale, and skirret as some examples of “unfamiliar vegetables” that are being introduced or reintroduced to the family of cooking vegetables.

·         In the case of tuberous chervil, for example, the vegetable has been forgotten after being identified in 1846 due to growing and production challenges: germination period, low crop yield, narrow window for the root to become edible in terms of size, vulnerability to saprophytic mushrooms that cause surface lesions, etc.

·         Agronomists are working on methods for improving upon these issues prompting the author to conclude (at the time of writing) that “the introduction of novel vegetables requires extensive research”.

PRESERVING MUSHROOMS

·         For button mushrooms to remain looking “fresh”, darkening of the skin lengthening of the stem, exposure of the ink-black gills, and “denaturing” of taste and texture must be avoided.

·         When button mushrooms are kept at cold temperatures, microbial and physiological degradation is minimized.  For example, when placed on display at 11 C in 90% humidity, the mushrooms remained presentable for 3-5 days.

·         Changes taking place in mushrooms under different conditions:

·         In the complete absence of oxygen Clostridium botulinum grow on mushrooms.

·         Increasing carbon dioxide concentration and decreasing oxygen concentration slows down the respiration rate of fungal cells and thus degradation.

·         Scientists carried out experiments to study the effect of different concentrations of oxygen and carbon dioxide. They observed a correlation between carbon dioxide concentration and its phytotoxic effect as this gas damages cell membranes which makes the cell vulnerable to darkening enzymes:

o   The darkening effect is minimized when the oxygen and carbon dioxide concentrations are lower than 10% [for both or each? Not clear.]

o   Texture is maintained when the carbon dioxide concentration is higher than 10% and oxygen concentration is lower than 10%.

o   Storing button mushrooms for a week at 10 C and 15% carbon dioxide prevents rupturing of the veil.

o   Higher carbon dioxide concentrations are better for keeping the cap closed.

o   High humidity causes faster degradation (keep bag open inside refrigerator).

o   The author concludes from the study that the optimal concentrations fall within 2.5-5% for carbon dioxide and 5-10% for oxygen.

·         To create and maintain exposure to these optimal concentrations, the team of scientists studied sealing in the mushrooms using two types of films:  microperforated polypropylene and stretchable polyvinyl chloride.  They found that the old PVC type was best at slowing down degradation perhaps because of its better protection against humidity.

·         [No explanation was given as to effects of carbon dioxide and oxygen]

TRUFFLES

·         “European truffles are all of the same species, but genetic analysis shows that Chinese truffles are something quite different.”

·         Genetic analysis was carried out on 200 samples of truffles from France and Italy.  Initial findings show that “satellite DNA sequences” differ substantially between species of the same genus but no genetic variability was observed in the samples.  This genetic homogeneity was explained by historical information indicating that the current population of black truffles is descended from a small population next to the Mediterranean that got trapped in the last Ice Age along with the trees on which they develop.  As the climate warmed, they recolonized the regions wherein the favored trees grow.  In 10,000 years, the species was able to reestablish itself but there was not enough time for evolution.

·         Chinese truffles grown in the Himalayas are sometimes passed off as the more expensive black European truffles.  Scientists asked whether the Chinese truffles are different from the black truffles because of different growing conditions or speciation.  Studies have shown that they are genetically different from the black truffles even though they look similar to a certain type of black truffle.

MORE FLAVOR

·         “Odorant molecules are trapped so that they may be better perceived.”

·         Odorant molecules are found in two distinct “physicochemical environments” in cooked meat:

o   Dissolved for the most part in the fat dispersed among the muscles of the cooked meat

o   In the liquid solution of the sauce

·         Odorant molecules from these two environments are released in different ways inside the mouth.

·         Factors that affect the rate and extent of release of these volatile odorant molecules include

·         temperature

·         the solvent used due to their different affinities for solvent molecules (oil, water, alcohol).

·         Binding the volatile odorant molecules to larger less volatile molecules increases their retention.  In an aqueous solution, amylose in starch molecules and gelatin for instance can wrap themselves around hydrophobic molecules.

·         Micro-Compartmentalization in which the odorant molecules are stored in membranes or vesicles that require a special action to release them.  For example, in a mixture of parsley, chervil, tarragon, and hives called fines herbes, the odorant molecules are released only after chewing which disrupts the cell membranes.  Emulsions, foams, gels, and pasta work in a similar way to retain odorant molecules until they are released by the chewing action.

·         Macro-Compartmentalization:  Marinating allows the flavor and odorant molecules to be retained by allowing them to penetrate the neat.  Decoction (concentrating the odorant and flavor molecules by evaporation), maceration, and infusion are other examples.

FRENCH FRIES

·         “A new kind of potato for frying, packaged raw, absorbs less oil than frozen fries.”

·         French fries made from fresh potatoes absorb less oil.  Frozen French fries that are pre-dried and pre-deep fried absorb more oil in re-frying because of the microscopic cracks created during the freezing process.

·         Chemists in France studies packaging methods for raw sliced potatoes under controlled atmospheric conditions.  One of the problems that need a solution for this type of packaging to be viable is preventing the browning process.  Some of the steps used to minimize browning are:

o   The peeling process must be carefully done under a stream of water to prevent damage to cells.

o   A very sharp knife should be used again to minimize rupturing of the cells.

o   Each slice must be kept at 4 C to slow down any cellular process.

o   The slices are drained by centrifugation or ventilation and then placed in an atmosphere of inert gas from which oxygen has been removed.

·         Results of this process of packaging:

o   The slices can be stored for 10days at 4 C without any changes.

o   Sugars accumulate on the potatoes however which cause Maillard reaction browning upon cooking

o   Similar amount of oil is absorbed as fresh potatoes and much less than pre-deep fried frozen slices.

o   Flavor and texture of the cooked fries are similar to those prepared from fresh potatoes.

·         To determine the best way to cook French fries, the ideal French fries must first be defined.  As the author states, these probably indisputable characteristics are:

o   Tender at the center

o   Crispy on the outside without too much browning

o   Minimal oil absorbed and greasiness

·         In the frying process, heat diffuses from the outside inward resulting in crust formation and cooking of the inside.

·         Structural properties and chemical transformations

·         As heat penetrates from the outside to the interior of the slice, the cells are disrupted releasing their starch granules in the heated water.  As this water evaporates from the surface, a crust forms.

·         Starch is not an efficient conductor of heat.  A slice placed in hot oil at 180 C does not reach an interior temperature of 85 C until after several minutes.  Thus, French fries that are placed in very hot oil starts to burn outside before the inside is cooked.

·         Starting with colder oil slows down the crust formation and causes more oil get absorbed.

·         The recommendation based on empirical studies,

MASHED POTATOES

·         “Proteins change the behavior of starch in water.”

·         Starch granules in flour are exposed to atmosphere because of the milling of grains whereas in potatoes, the starch granules are in a watery environment.

·         Starch is not completely soluble in water; amylopectin, the branched polymer, is not at all soluble in water while linear amylose is only soluble starting at 55 C.

·         Flour acts as a thickener [increasing viscosity] in sauces because when it is added to hot sauce liquid, the amylose dissolves in the liquid while the insoluble amylopectin absorbs water and expands. The presence of dissolved amylose and starch granules causes the liquid to become more viscous.  When cooled down, the sauce forms the gel as the amylose molecules combine and trap water, starch granules, and other dissolved compounds.

·         When the protein casein is present, they reduce the amount of amylose that dissolves in the liquid and decrease their swollen size [Why?]. [The next part I am not sure I understand either.]  “Casein subsequently brings about a separation in the water phase: Protein-enriched water droplets separate from the rest of the sauce, which is then enriched by amylose in a continuous phase.  This increase in amylose concentration favors its gelatinization.”

·         When milk is added to mashed potatoes, the casein protein in milk “limits the swelling of starch granules yields a smoother, more pleasing consistency”.

ALGAL FIBERS

·         “Algae contain fibers whose nutritional value is comparable to that of vegetable fibers.”

·         Fibers are macromolecules typically consisting of chains of monosaccharides and make-up the cell wall of plants.  Humans do not carry the enzyme for digesting fibers. 

·         An old classification system for fibers is based on the degree of solubility in response to various enzymatic treatments.  The water-soluble fibers include

o   certain pectins (fruit polysaccharides that cause gelling)

o   algal polysaccharides

o   certain kinds of hemicellulose [cell wall components composed of polysaccharides simpler than cellulose]

·         The insoluble fibers include:

o   Cellulose

o   Other kinds of hemicelluloses

o   Lignin

·         Many of the soluble fibers have interesting rheological properties [relating to deformation and flow of matter] and “were thought to reduce the blood concentration of cholesterol and to act on the metabolism of glucids and lipids”.

·         Insoluble fibers are thought to cause more rapid bowel movement.

·         The classification of fibers in algae has been refined using a modified version of the gravimetric method. In this method, the polysaccharide fibers are precipitated after removing starch and proteins by enzymatic treatment of the algae.

·         In 1991, a group of scientist used this method to determine the amount of polysaccharides dissolved in a solution prepared to simulate the environment in the digestive tract.

·         In studying wakame ( a type of brown seaweed), they found that it contains as much as 75% [by mass?] dietary fiber compared to 60% in Brussels sprouts (the root vegetable richest in fiber).

·         Study of how fibers behave in the digestive tract show a comparison of two different algal plants:

o   Laminaria digitata:  glucose polymers (mostly cellulose) known as laminarins are soluble in very acidic solution only while the alginates dissolve in neutral solutions [alginates are insoluble gelatinous carbohydrates].

o   Dulse (common red seaweed):  contains fibers that “seem to be continuously solubilized in the successive sections of the digestive system”.

·         Algal fibers are being proposed as an abundant source of fiber much like fiber from beets, cereals, and fruits are vegetable of sources of fiber for breakfast foods.

CHEESES

·         “Commercial protection requires several kinds of analysis”

·         The human nose has “no rival” when it comes to detecting trace amounts of molecular compounds of an odorant nature.

·         This chapter describes methods and criteria used by qualified testers to objectively and consistently judge the qualities of cheese: superficial, mechanical, and geometric characteristics, sensations produced in the mouth.  Perceptions and intensities are stated based on comparison to a reference class of basic textures associated with familiar textures of apples, a cracker, a banana peel, etc.

FROM GRASS TO CHEESE

·         “Diet contributes to the quality of cows’ milk.”

·         Analysis of volatile compounds in Gruyere made in Switzerland showed distinction between mountain pasture cheeses and those from the plains.  Mountain pasture cheeses contain higher concentrations of the fragrant molecules which belong to the class of terpenes (e.g. limonene, pinene, nerol).

·         A group of scientists found that dietary characteristics contribute to the sensory characteristics of the cheese: the cheeses from the southern region were shinier and less yellow with a more intense, fruitier, and spicier taste.   The scientists speculate that these differences may be due to the molecular make-up of the cow’s foraging diet.  For example, plants common in the northern region are known to contain subtoxic compounds that make mammary tissue cells more permeable to enzymes that alter the quality of cheese.  The flora of microorganisms in the soil might also contribute to these differences.

THE TASTE OF CHEESE

·         “Lactic acid and mineral salts give goat cheese its distinctive taste.”

·         The aqueous phase of cheese consists mostly of lactose, lactic acid, mineral salts, amino acids, and peptides.

·         Different solutions containing with one or more of the above removed were prepared to determine what each one contributes to the taste of cheese.

·         Sensory evaluations by qualified testers showed that:

o   only lactic acid and mineral salts contributed to the taste

o   acidity of the cheese is due to hydrogen ions from lactic and phosphoric acids

o   saltiness is due to sodium, potassium, calcium, and magnesium chlorides and sodium phosphate

o   some bitter taste came from calcium and magnesium chlorides although it was partially masked by sodium chloride mixtures and by phosphates

o   very very weak sweet and umami tastes

·         Other general findings:

o   No taste can be traced back to one single compound

o   “different sapid compounds have both inhibiting and enhancing effects on one another”

YOGURT

·         “A smoother product can be obtained by modifying its milk composition and fabrication process”

·         Milk is an emulsion wherein fat globules and casein micelles are dispersed in water in which lactose and other compounds are dissolved.

·         Addition of yogurt to milk to milk causes curdling because microorganisms in the yogurt metabolize lactose into lactic acid.  The increased acidity of the milk causes the casein micelles to aggregate trapping water, fat globules, and microorganisms.

·         The texture and consistency of milk was studied to understand the effect of increasing the concentration of fat and protein.  Results showed that changing the concentration of fat and protein did not have any noticeable effect on the size of the lat globules.  The number of fatty droplets grew with a higher fat concentration but there was always enough proteins to coat the fatty globules and emulsify them.

·         Another factor studied is the addition of tensioactive molecules (amphiphilic) in an attempt to control the aggregation process.  The tensioactive molecules had different effects depending on when they were added.  When they were added after emulsion has already taken place, the tensioactive molecules had no effect on the milk proteins that coat the fatty droplets and the extent of aggregation did not change.  Adding the same molecules at the point of emulsification changed the distribution of proteins and reduced the extent of aggregation.

MILK SOLIDS

·         “How to gelatinize milk without destabilizing it”

·         Cheeses are milk “preserves” made by disrupting the emulsion and removing the water it contains in the form of whey.

·         Yogurt is made from milk by heating it in the presence of bacteria (lactobacillus bulgaricus and streptococcus thermophilus.  These bacteria metabolize the lactose into lactic acid acidifying the liquid and creating a gel when a network (?) is formed throughout the liquid.

·         Examples of gelatinizing and thickening agents used in milk:  gelatin (extracted from animal bones), starch, carrageenans and alginates from algae, galactomannans (guar and carob gums) come from seeds, pectins come from plants, and xanthan gum is obtained from fermented starch.

·         Except for gelatin, all of these substances above contain polyosides (I have never encountered this term before but I looked it up and it sounds like it is mostly a French term which refers to a specific type of polysaccharide), “compounds of the same chemical family as the sugars”, containing many –OH groups which bond to water molecules and cause the thickening effect.

·         In milk, polyosides are thought to bond not just to casein proteins but other dissolved proteins.

·         In studying the non-intuitive effect of polyosides destabilizing the emulsion in milk, researchers found “high concentrations of polyosides produce a phase separation:  the polyosides come together in certain areas of the solution and the casein proteins in others”.

·         Two Japanese scientists discovered the mechanism known as depletion-flocculation that occurs in particle suspensions:  In solutions and particle suspensions, equilibrium exists when particles repel each other more than attract each other.  When large polymers are added, this equilibrium is disrupted because they cannot distribute themselves easily between adjacent particles creating null spaces.  Water flows out of these null spaces (called a depletion zone) in order to “reduce the polymer concentration outside it.  When the water diffuses in this way the particles are moved closer together.  In milk, the casein particles thus form a flocculent mass forming the dreaded lumps.”  This phenomenon is exacerbated the higher the concentration of polyosides added.

SABAYONS

·         “The foam of a sabayon is stabilized by the coagulation of the egg”

·         Nothing new of interest in this chapter’s discussion of the foaming process.

FRUITS IN SYRUP

·         “How to optimize the sugar concentration of syrups for preserving fruits.”

·         Osmosis plays a role in determining how much sugar to add when making fruit syrups.  Too little sugar in the water causes the fruit to absorb water and swell; too much sugar causes the fruit to shrink as water leaves the fruit where the sugar concentration is lower. 

·         The author suggests to add the fruit to the water and gradually add sugar until the fruit pieces just start to float (density about the same).  This ensures that the resulting sugar solution outside has a concentration close to that of the fruit sugar.

FIBERS AND JAMS

·         “Proteins can be recovered from the fibrous matter of fruits and vegetables by extrusion cooking.”

·         Pectins are molecules that make up the cell wall along with cellulose and other polysaccharides.  Many fruits have pectin but not cereals.  Pectins are recovered from plant fibers by heating them in an acidic solution which causes them to detach and precipitate.  The resulting pectin can be used as a gelatinizing or thickening agent and also to coat potato chips.

·         This hot acid method is not the most optimal method because it can degrade the protein by disrupting bonds with their constituent sugars and alter their chemical structure.

·         In this chapter, the author describes an apparatus that can extract pectin from plant fibers by extrusion.

·         Not all pectins can cause gelling to happen.  Pectins from limes, lemons, oranges, and apples are efficient gelatinizing agents whereas beet pulp pectin does not gelatinize.  It turned out that the degree of esterified –COOH group is correlated with pectin’s ability to bond to other pectin molecules causing gelatinization.

·         Pectins bond strongly with metal ions, e.g. copper ions from copper pots.

THE WHITENING OF CHOCOLATE

·         “To keep chocolate from turning white, keep it chilled”

·         The whitening of chocolate is due to the migration to and subsequent crystallization of low melting point triglycerides (at least one double bond in the fatty acids) on the surface.

CARAMEL

·         “The molecules of caramelization finally identified”

·         Maillard reactions involve both amino acids and sugars in producing flavor, aroma and color molecules.  Caramelization only involves sugars.

·         Although caramel has been known since the time of Seneca in 65 BC, it was only recently that its chemical composition has been elucidated.

·         In the twentieth century, caramel was thought to contain humic acids which are “poorly understood reducing compounds whose tanning properties are also found in lignite.  The volatile component was found to contain 5-hydroxymethyl-2-furladehyde and about 20 other compounds including formaedehyde, acetaldehyde, methanol, ethyl lacate, and maltol that contribute to its “penetrating odor”.

·         In 2989, the nonvolatile part was partially determined to contain fructose dianhydrides.  Furthermore, they were able to determine the chemical transformations taking place which involve the separation of sucrose into glucose and fructose and the formation of oligosaccharides. 

·         The discovery of these oligosaccharides in caramel is commercially significant because the this may allow the classification of polydextroses (a form of oligosaccharide) as naturally occurring thereby removing them from being subjected to regulations of synthetic molecules.

BREAD AND CRACKERS

·         “The mechanical behavior of bread resembles that of plastic materials”

·         In this chapter, the author discusses some studies done to determine optimal temperatures for cooling down bread to slow down its degradation.  It starts off by explaining the polymer nature of bread, made from starch which is a branched polymer of amylopectin and linear amylose.

·         When polymers are cooled, they first turn rubbery when some chains crystallize and others are still mobile.  Lower than the temperature of vitreous transition, all the chains crystallize in an amorphous rigid arrangement just like in glass.  The more rapid the cooling, the more the vitreous form dominates.

·         As long as the temperature is above the vitreous transition temperature of -20 C, the bread stays in a rubbery form even though water has frozen (acts as a plasticizer).  Between 0 to -20 C, bread still undergoes structural changes.  Therefore, the preserve the textural characteristics of bread, it must be frozen below -20 C.

THE TERROIRS OF ALSACE

·         “The openness of the landscape is a crucial factor”

·         In this chapter, the author discusses some studies designed to characterize the conditions that define a terroir, the overall natural environment of a winegrowing region.

·         In growing grapes, the focus is on conditions for planting grapevines that favor the growth of berries rather than leaves or branches and the accumulation of sugars for fermentation and aromas.

·         In one study, it was found that the best terroirs are one where there is a regular supply of water and only moderate droughts to encourage the early ripening of grapes.  In another study, it was found that “the more rapidly the soil heats up in the spring, the earlier the vine develops and the more favorable the landscape is to successful cultivation”.

·         “In all the wine-growing regions studied, water nourishment conditions played a major role in determining, among other things, the length of time between the fruiting of the vine and the ripening of the grapes.  Maturation comes late when water is plentiful because the vine produces leaves rather than berries.  When the supply of water is insufficient maturation is delayed as well…”.

·         In one study of aromas, the researchers detected “a high degree of variability in terpene alcohol content and the oxides of these alcohols”.

LENGTH IN THE MOUTH

·         “Enzymes in saliva amplify an important aromatic component of wines made from the Sauvignon Blanc grape.”        

TO BE CONTINUED