Stability of Glutamine and Pyroglutamic Acid under Model System Conditions: Influence of Physical and Technological Factors

The stability of glutamine and pyroglutamic acid as regards pH, temperature and oxygen was studied during storage and two thermal processings, the residual products and those which appeared being determined. Contrary to glutamic acid, the two derivatives are labile below pH 2 and above pH 13 and alteration occurs much faster. Temperature increase promotes this phenomenon. Glutamic and pyroglutamic acids convert reversibly into one another, more or less quickly and completely according to the conditions. Glutamine changes during heating in two steps, first into glutamic acid, then into pyroglutamic acid if the pH values are not extreme. The influence of pH conditions on the direction and the rate of the reaction are indicated.     

EFFECTS OF CYCLOPROPENOID FATTY ACIDS (BAOBAB SEED OIL) ON THE FATTY ACID PROFILE OF LIPIDS FROM DIFFERENT TISSUES IN THE RAT

Rats were fed for 8 weeks a diet containing either Baobab seed oil (FBO) rich in cyclopropenoid fatty acids (CPFA) or heated oil (HBO) devoid of CPFA. In FBO rats, compared to controls (CO), the monounsaturated fatty acid content of adipose tissue lipids, liver triacylglycerols, liver and adrenal cholesteryl esters and liver, kidney, adrenal phospholipids were highly decreased to the benefit of saturated fatty acid content. In cholesteryl esters and phospholipids, the arachidonic acid (20:4 n-6) content was markedly decreased, especially in adrenals. In adrenal cholesteryl esters, adrenic acid (22:4 n-6) content was decreased more than its precursor. The effects of HBO on the tissue lipid fatty acid profile were practically absent. It is concluded that inhibition of fatty acid desaturation by CPFA previously demonstrated in vitro , was reflected in vivo in tissue lipid fatty acid composition.     

CONSUMPTION AND PLATE WASTE OF REGULAR AND TOTAL TRIM ROASTED PORK LOINS

Regular or total trim roasted pork loin was served to 175 diners to determine the effects of trim level and serving size on consumption and plate waste. Diners ate more total trim pork because they selected similar serving sizes of the two fat trim levels, yet trimmed excess fat from regular trim pork. Therefore, close trimming of pork may increase consumption. Caloric intakes were similar for diners served regular and total trimmed pork because diners trimmed separable fat from fatter pork. Shifting from a fatter to a closely trimmed product may not reduce cholesterol consumption because of similar cholesterol contents of cooked separable lean and fat. To reduce the fat content of cooked muscle, trim subcutaneous and intermuscular fat before cooking.     

Formation of Pyrazines by Chitin Pyrolysis

Chitin, poly-β-(1–4)-N-acetyl-D-glucosamine, was heated at 300-500°C for 5-60 min to examine the potential of pyrazine formation from chitin pyrolysis. 2-Methyl-, 2,3-dimethyl- and 2,3,5-trimethyl-pyrazine were formed at 300°C and additionally, 2,5-dimethylpyrazine was found with increasing pyrolysis temperature up to 500°C. During 60 min of pyrolysis more than twice as much 2,3,5-trimethylpyrazine as 2,5-dimethylpyrazine was developed. Thus, altering time and temperature of chitin pyrolysis could be useful for the development of certain pyrazines that have food flavor applications.     

Acidic Characteristics of Fermented and Dried Cocoa Beans from Different Countries of Origin

Thirty-nine fermented and dried cocoa bean samples from 13 countries were evaluated for pH, titratable acidity and concentrations of volatile and nonvolatile acids. The correlation coefficient between pH and log₁₀ titratable acidity was -0.94. Cocoa beans from Brazil and Far Eastern countries were highly acidic while those from Central American and South American countries were low in acidity. Samples from West African countries were intermediate with titratable acidity values from 0.12 to 0.15 meq NaOH/g sample and pH values from 5.20 to 5.49. Highly acidic beans were characterized by high concentrations of acetic and lactic acids. The high correlation between acetic acid and both pH (r=0.86) and titratable acidity (r = 0.91) indicated that this acid could be primarily responsible for high acidity in cocoa beans.     

BACTERIAL ADHERENCE AND VIABILITY ON CUTTING BOARD SURFACES

The adherence and viability of Escherichia coli inoculated onto the surfaces of plastic cutting boards and new and used wood cutting boards were evaluated. Most of the inoculum was recovered from all surfaces after resident drying times of 5 min and from plastic surfaces at 24 h. When the exposure time was extended to 2 h, > 90% of the cells placed on new and used dry wood surfaces were not recovered after vigorous rinsing. Scanning electron microscopy showed that the bacteria resided within the structural xylem fibers and vegetative elements of the wood. After resident drying times of up to 2 h, almost 75% of the adherent bacteria on the wood surfaces were viable, as defined by a nalidixic acid direct viable count procedure. Microcosm studies showed no intrinsic growth-supporting or toxic properties of the cutting board materials. Bacteria that adhered to plastic surfaces were more easily removed by low-temperature washing than were cells that adhered to wood surfaces. These studies demonstrated that bacteria adhering to wood surfaces resided within the structural and vegetative elements of the wood's xylem tissues and were viable; wood was more retentive than plastic; penetration of the inoculum liquid promoted cell adherence to the wood matrix; and conditioning of wood with water before inoculation interfered with bacterial adherence.     

Differentiation of Australian wine isolates of Oenococcus oeni using random amplified polymorphic DNA (RAPD)

Intraspecific variation of Oenococcus oeni , the preferred lactic acid bacteria species for inducing malolactic fermentation in wine, was studied using the randomly amplified polymorphic DNA (RAPD) strain fingerprinting technique. Ten of fifteen isolates of O. oeni from Australian wineries situated in different wine regions could be distinguished by the RAPD technique. Strains of O. oeni which originated from the same winery were either indistinguishable or closely related to each other. Six different commercially available O. oeni strains could be differentiated with the four RAPD primers used and their genetic similarity determined. Analysis of O. oeni present in wines from a single source of fruit (Cabernet Sauvignon, vintage 2002) that underwent spontaneous malolactic fermentation revealed wide genetic variation amongst the isolates. Each fermentor contained several different O. oeni strains, which were present throughout alcoholic and malolactic fermentation. These data highlight the sensitivity of RAPDs when suitable primers are applied to O. oeni of unknown genetic origin, thus enabling O. oeni strains with desirable sensory and fermentation properties to be genetically analysed.     

ESTIMATION of HEAT of MOISTURE SORPTION and IMPROVED CRITERIA FOR EVALUATING MOISTURE SORPTION ISOTHERM EQUATIONS FOR FOODS

Heat of sorption of moisture on foods can be estimated from sorption isotherm equations having both moisture and temperature as independent variables. Sorption thermodynamics dictate that the heat of moisture sorption should decrease with increased moisture concentration, or increased temperature of food, provided no biological, chemical or other changes occur during sorption. This fact, and the Clausius-Clapeyron equation were used to derive two analytical formulae to evaluate the reliability of moisture sorption equations in the calculation of heat of sorption. As examples, Chung and Pfost, modified Harkins and Jura, modified Henderson, and Guggenheim-Anderson-De Boer equations at specified conditions were analyzed.     

Simultaneous Determination of Neutral Sugars and Uronic Acids in Hydrocolloids

An improved gas-chromatographic method for the simultaneous determination of neutral sugars and uronic acids in hydrocolloids or industrial gums was developed. The procedure involved methanolysis with 0.5M methanolic HCl followed by trimethylsilylation. This method was simplified over other derivatization methods to make it suitable for the routine analysis of hydrocolloids or other polysaccharides which contain uronic acids. The usefulness of this method was demonstrated by analysis of commercially available hydrocolloids. The described method was sensitive enough to identify some of the minor sugar components which were not easily identified by other derivatization methods.     

ANTHOCYANINS OF BEAUTY SEEDLESS GRAPES

Beauty Seedless grape pigments were isolated and identified by chromatographic, spectral and chemical properties. The pigments were identified as delphinidin-3-glucoside, petunidin-3-glucoside, malvidin-3-glucoside, peonidin-3-glucoside, malvidin-3-glucoside acylated with caffeic acid and malvidin-3-glucoside acylated with p-coumaric acid. Beauty Seedless grapes contained 62 mg anthocyanins per 100g fresh grapes and malvidin derivatives accounted for 73% of the total anthocyanins.