INSTABILITY OF SODIUM NITRITE IN A CHEMICALLY DEFINED MICROBIOLOGICAL MEDIUM

Mixtures of sodium nitrite, amino acids and ascorbic acid at pH 6.3 or 7.2 were filter sterilized or heated for various times at 121°C. Samples were analyzed for nitrite concentration immediately after treatment and after storage at 37 or 43°C. Heating the complete medium for 15 min at 121°C reduced the nitrite concentration by 30–50% independent of the initial nitrite concentration. Storage of complete filter sterilized medium at 43°C for 18–24 hr resulted in 50–65% loss of nitrite while in heat sterilized medium the loss was as great as 90%. None of the 19 amino acids stored individually with sodium nitrite at 37°C for up to 4 hr affected the nitrite concentration, whereas ascorbic acid resulted in total disappearance of nitrite. During heating at 121°C of the 19 amino acids only cystine resulted in any significant nitrite loss after 15 min of treatment while ascorbic acid effected total nitrite disappearance after 5 min. The defined medium containing nitrite demonstrated inhibitory activity against seven strains of Clostridium perfringens.     

Rheology and Oxidative Stability of Whey Protein Isolate-Stabilized Menhaden Oil-in-Water Emulsions as a Function of Heat Treatment

ABSTRACT:  Menhaden oil-in-water emulsions (20%, v/v) were stabilized by 2 wt% whey protein isolate (WPI) with 0.2 wt% xanthan gum (XG) in the presence of 10 mM CaCl₂ and 200 μM EDTA at pH 7. Droplet size, lipid oxidation, and rheological properties of the emulsions were investigated as a function of heating temperature and time. During heating, droplet size reached a maximum at 70 °C and then decreased at 90 °C, which can be attributed to both heating effect on increased hydrophobic attractions and the influence of CaCl₂ on decreased electrostatic repulsions. Combination of effects of EDTA and heat treatment contributed to oxidative stability of the heated emulsions. The rheological data indicate that the WPI/XG-stabilized emulsions undergo a state transition from being viscous like to an elastic like upon substantial thermal treatment. Heating below 70 °C or for less than 10 min at 70 °C favors droplet aggregation while heating at 90 °C or for 15 min or longer at 70 °C facilitates WPI adsorption and rearrangement. WPI adsorption leads to the formation of protein network around the droplet surface, which promotes oxidative stability of menhaden oil. Heating also aggravates thermodynamic incompatibility between XG and WPI, which contributes to droplet aggregation and the accumulation of more WPI around the droplet surfaces as well.     

Effect of heat on the fatty acids and aldehydes of veal meat phospholipids

Reactions involving phospholipids contribute considerably to the flavour and aroma of cooked meat. The effect of heat on the fatty acids and fatty aldehydes of phospholipids from veal was studied using aqueous model systems wherein extracted phospholipid fractions were heated in the presence or absence of ribose or glycine. After 1 h at 132°C, ethanolamine-containing phospholipids rapidly lost most of their component aldehydes but not their fatty acids, whereas choline-containing phospholipids lost their aldehydes much more slowly. In both cases, the presence of ribose or glycine had little effect on the loss of aldehydes. In the meat itself, after heating at 132°C, there was a 90% loss of aldehydes which was similar for both the ethanolamine- and choline-containing phospholipids, but the latter lost fatty acids more slowly than the former.     

Antifungal activity stability of flaxseed protein extract using response surface methodology

ABSTRACT:  The stability of the antifungal activity of flaxseed ( Linum usitatissimum ) protein extract was evaluated in this study. Response surface methodology (RSM) using Box–Behnken factorial design was used to evaluate the effects of treatment variables, that is, temperature (50 to 90 °C), time (1 to 29 min), and pH (2 to 8), on the residual antifungal activity (RAA) against Penicillium chrysogenum , Fusarium graminearum , Aspergillus flavus , and a Penicillium sp. isolated from moldy noodles. Regression analyses suggested that the linear terms of the temperature and time had significant ( P < 0.05) negative effects on the RAA against all test fungi, whereas that of pH had a significant ( P < 0.1) positive role on the RAA of all 3 fungi. In addition, the RAA was significantly ( P < 0.05) affected by the quadratic terms of time for all fungi, and the quadratic term of temperature played a significant ( P < 0.1) role on RAA against F. graminearum. One interaction term (temperature-pH) was found to significantly ( P < 0.1) affect the RAA against both Penicillium strains tested. The results indicated that ≥ 90% antifungal activity was lost after the protein extracts were heated at 90 °C for 8 min except for F. graminearum . At pasteurization condition, ≥ 50% activity was retained except for P. chrysogenum . The results also suggested that neutral and alkaline pH favored the antifungal activity stability of the protein extracts. Thus, flaxseed protein might be promising if used as a preservative in foods with neutral or alkaline pH requiring mild heat treatments.     

Effect of heat treatment on curcuminoid, colour value and total polyphenols of fresh turmeric rhizome

Studies were undertaken to examine the effect of heat treatment on total phenolic content (TPC), colour value (yellowishness and brightness), polyphenol oxidase (PPO) activity and curcuminoid of fresh turmeric rhizome. Fresh turmeric rhizomes were subjected to heat treatment at different temperatures (60–100 °C) for different durations (10–60 min), causing a reduction in browning which was evident from the improved yellowishness and brightness. Activity of PPO was also decreased during heat treatment and PPO was almost inactivated when heated at 80 °C for 30 min. TPC of heat-treated turmeric after drying (powder) is significantly higher than that after the fresh process. TPC values increased gradually when samples were heated from 60 to 80 °C. At 90 and 100 °C, TPC values were almost identical. Maximum brightness and yellowishness were obtained when the turmeric was heated above 80 °C. Quantitation of curcuminoids in the turmeric sample was made with high performance thin layer chromatography (HPTLC). There was no significant change in the concentration of curcuminoids among the heat-treated samples. But in the sun-dried samples, a significant reduction in curcuminoid concentration was observed.     

Degradation of white wine haze proteins by Aspergillopepsin I and II during juice flash pasteurization

Bentonite is commonly used to remove grape proteins responsible for haze formation in white wines. Proteases potentially represent an alternative to bentonite, but so far none has shown satisfactory activity under winemaking conditions. A promising candidate is AGP, a mixture of Aspergillopepsins I and II.; a food grade, well characterized and inexpensive protease, active at wine pH and at high temperatures (60-80°C). AGP was added to two clarified grape juices with and without heat treatments (75°C, 1min) prior to fermentation. AGP showed some activity at fermentation temperatures (≈20% total protein reduction compared to control wine) and excellent activity when combined with juice heating (≈90% total protein reduction). The more heat stable grape proteins, i.e. those not contributing to wine hazing, were not affected by the treatments and therefore accounted for the remaining 10% of protein still in solution after the treatments. The main physicochemical parameters and sensorial characteristics of wines produced with AGP were not different from controls.     

Heat treatment of scallop adductor muscle using superheated steam

ABSTRACT:  Scallop ( Patinopecten yessoensis ) adductor muscles were heated using superheated steam (150 and 200 °C), boiling (98 °C), and normal steaming (95 °C). The amounts of amino acids, water-soluble peptides, and nucleotides, expressed as extractive nitrogen in scallop products, are very important elements of quality and taste. After 15-min heating of scallop muscles with normal steaming and boiling, respective losses of 50% and 64% of the extractive nitrogen were observed. However, most extractive nitrogen (> 86%) remained in the scallop muscles treated with superheated steam at 150 and 200 °C. Protective effects of superheated steam against elution loss of nitrogen compounds were also observed in amino acid analyses of the heated products. The scallop-muscle surface temperature during treatment with superheated steam increased more quickly than that with normal steaming and boiling. The rapid water loss and the surface protein denaturation engendered formation of a 30-μm-thick film covering the surface, which prevented extractive nitrogen loss from internal tissues. Superheated steam treatment at 200 °C caused browning, surface shrinkage, and 47% weight loss. In marked contrast, the appearance and the weight loss of sample treated at 150 °C were almost the same as those of normal steaming and boiling-treated samples. These results suggested that superheated steaming at 150 °C is an optimal heat treatment of scallop adductor muscles.     

Proteins recovered from milks heated at alkaline pH values

Approximately 95% of available nitrogen can be precipitated from milk on adjustment to pH 4.6 after heating at 90°C × 15 minutes at its natural pH and pH 7.5, while 89% can be precipitated after heating at pH 10.0 at 60°C × 3 minutes. Non-recovered protein includes some serum albumin, β-lactoglobulin, α-lactalbumin and proteose peptones. Protein isolates precipitated from milk heated at pH >7.0 are more soluble in the pH range 6.0–7.0 than those precipitated from milk heated at its natural pH. Whey proteins complex onto the casein micelles after heating milk at its natural pH, while on heating at pH >7.0 whey proteins appear to interact with k-casein in the serum phase. When N-ethylmaleimide is present in milk during heating the percentage protein recovered on pH 4.6 precipitation is decreased, confirming that disulphide linkage is involved in complex formation. However, addition of β-mercaptoethanol to recovered isolates did not result in dissociation of the casein/whey protein complex, suggesting that forces other than disulphide bonding are also involved in maintaining the complex.     

MOLECULAR PROPERTIES OF POSTMORTEM MUSCLE. 10. Effect of Internal Temperature and Carcass Maturity on Structure of Bovine Longissimus

SUMMARY– A study was carried out with light and electron microscopic techniques to discover the effect of heating and carcass maturity upon the connective tissue and myofibrillar proteins of longissimus from veal (5–6 months), A (12–20 months) and D (54–60 months) maturities. Longissimus was heated to internal temperatures of 1) 50°C; 2) 60°C; 3) 70°C; 4) 80°C and 5) 90°C. Light microscopy indicated that connective tissue fibers increased in size and degree of aggregation with carcass maturity. Also, the more aggregated fibers from D maturity were more heat resistant than the less aggregated fibers of veal and A maturity. Endomysial connective tissue shrinkage was initiated at 50°C and it was completed at approximately 70°C. On the other hand, perimysial connective tissue shrinkage required internal temperatures of 70°C and higher before any significant fiber changes were observed. However, if endomysial and perimysial connective tissue fibers showed similar degrees of aggregation, they appeared to react similarly to heat regardless of maturity group. Electron and phase contrast microscopy showed that myofibrillar proteins compressed and sarcomeres shortened at 50°C. Heating to 60°C caused loss of M-line structure, initiation of disintegration and coagulation of thin and thick filaments and further myofibrillar protein shrinkage. Heating to 70 and 80°C caused more disintegration of thin filaments and coagulation of thick filaments. At 90°C, an amorphous structure resulted, but regardless of the internal temperature the principal banding features of the sarcomere could be identified. These changes are discussed in relationship to changes in meat tenderness.     

The effect of bentonite fining at different stages of white winemaking on protein stability

Background and Aims: Bentonite fining to remove protein is the most widely used treatment to prevent protein haze in white wines. Bentonite can be added at different stages during winemaking. This study aimed to determine the best time to add bentonite. Methods and Results: Unstable juices were vinified after bentonite fining of juice, or with bentonite added either early or late in fermentation. Different addition rates of bentonite were used and bentonite was either added in one or two additions. Fermentation rates were observed and protein stability and bentonite fining rates of the resultant wines were determined. Conclusions: Adding bentonite during fermentation or fining finished wines was the most efficient option in terms of amounts of bentonite required. Fermenting with bentonite present also may increase fermentation rates. Significance of the Study: Using the least bentonite necessary for heat stability is important for winemakers for quality, cost and environmental reasons. This study describes ways in which bentonite addition rates can be minimised.     

Physical Stability of Whey Protein-stabilized Oil-in-water Emulsions at pH 3: Potential ω-3 Fatty Acid Delivery Systems (Part A)

ABSTRACT: The oxidative stability of polyunsaturated lipids can be improved by incorporating them in oil droplets surrounded by positively charged whey protein isolate (WPI) membranes. This study dealt with the factors that influence the physical properties of WPI-stabilized oil-in-water emulsions at pH 3. Emulsions containing 5 to 50 wt% corn oil and 0.5 to 5.0 wt% WPI (protein-to-oil ratio of 1:10) were prepared at pH 3. The apparent viscosity of the emulsions increased appreciably at oil concentrations ≥ 35 wt%; however, the particle size was relatively independent of oil concentration. The influence of NaCl (0 to 250 m M ) on the physical properties of 28 wt% emulsions was examined. Significant increases in mean particle size, apparent viscosity, and creaming instability occurred at ≥150 m M NaCl, which were attributed to flocculation induced by screening of the electrostatic repulsion between droplets. The influence of heat treatment (30°C to 90°C for 30 min) on 28 wt% emulsions was examined in the absence and presence of salt, respectively. At 0 m M NaCl, heating had little effect on the physical properties of the emulsions, presumably because the electrostatic repulsion between the droplets prevented droplet aggregation. At 150 m M NaCl, the mean particle diameter, apparent viscosity, and creaming instability of the emulsions increased considerably when they were heated above a critical temperature, which was 70°C when salt was added before heating and 90°C when salt was added after heating. These results have important implications for the design of WPI-stabilized emulsions that could be used to incorporate functional lipids that are sensitive to oxidation, for example, ω-3 fatty acids.     

Isolation and identification of protease-producing psychrotrophic bacteria from dairy products in India

Of the 259 proteolytic psychrotrophic bacterial cultures isolated from different dairy products produced at the National Dairy Research Institute, 39 cultures exhibited more than 150 units/ml protease activity. These isolates were identified and grouped into five genera, viz ., Pseudomonas spp ., Flavobacterium spp ., Alcaligenes spp ., Micrococcus spp., and Staphylococcus spp. The culture supernatants from six isolates retained more than 50% enzyme activity after heating at 50° C for 10 min, protease of Pseudomonas sp. 8–25 having maximum heat resistance.     

Preventing protein haze in bottled white wine

Slow denaturation of wine proteins is thought to lead to protein aggregation, flocculation into a hazy suspension and formation of precipitates. The majority of wine proteins responsible for haze are grape‐derived, have low isoelectric points and molecular weight. They are grape pathogenesis‐related (PR) proteins that are expressed throughout the ripening period post véraison, and are highly resistant to low pH and enzymatic or non‐enzymatic proteolysis. Protein levels in un‐fined white wine differ by variety and range up to 300 mg/L. Infection with some common grapevine pathogens or skin contact, such as occurs during transport of mechanically harvested fruit, results in enhanced concentrations of some PR proteins in juice and wine. Oenological control of protein instability is achieved through adsorption of wine proteins onto bentonite. The adsorption of proteins onto bentonite occurs within several minutes, suggesting that a continuous contacting process could be developed. The addition of proteolytic enzyme during short term heat exposure, to induce PR protein denaturation, showed promise as an alternative to bentonite fining. The addition of haze‐protective factors, yeast mannoproteins, to wines results in decreased particle size of haze, probably by competition with wine proteins for other non‐proteinaceous wine components required for the formation of large insoluble aggregations of protein. Other wine components likely to influence haze formation are ethanol concentration, pH, metal ions and phenolic compounds.     

IDENTIFICATION AND CHARACTERIZATION OF SOME OXIDIZING ENZYMES OF THE MC FARLIN CRANBERRY

SUMMARY– Enzyme extracts were prepared from acetone powders with and without phenol-binding agents such as polyethylene glycol (PEG) and polyvinylpyrrolidone (PVP) and buffered PVP. The acetone-PVP combination was found most effective in reducing the polyphenolic content of the enzyme extract. Highest specific activity was obtained by using a buffered PVP extract. The pH optimum of cranberry peroxidase activity was 6.0. Heat inactivation of cranberry peroxidase was determined to follow first order kinetics. There was 90% destruction at 70, 80, and 90°C requiring 9.40, 1.60, and 0.47 min of heat treatment, respectively. Activation energy for the thermal inactivation of cranberry peroxidase was observed to be 37.2 kcal/mole. Guaicol, o-phenylene diamine (OPDA), and pyrogallol were tested for their sensitivity to cranberry peroxidase with OPDA determined as most sensitive. The pH optimum for catalse activity was found to range from 7.5 to 9.2. Kinetics for the heat inactivation of cranberry catalase was observed not to be of the first order nor zero order. Approximately 50% of the catalase activity was inactivated after heating for 17, 1.8, and 0.6 min at temperatures of 50, 60, and 70°C, respectively. The pH optimum for cranberry polyphenolase activity was determined to be 7.0. Heat inactivation of cranberry poly-phenolase was found to follow first order kinetics. There was 90% destruction at 50, 60, and 70°C requiring 15.85, 7.05, and 1.37 min of heat treatment, respectively. The activation energy for the inactivation of cranberry polyphenolase was observed to be 27.7 kcal/mole.     

RHEOLOGICAL PROPERTIES OF WHEY PROTEIN CONCENTRATE GELS

The rheological properties of heat whey protein concentrate gels were studied by dynamic oscillation rheometry. A whey protein concentrate of 75% protein was used to make solutions of 10.3, 12.5 and 14.5% protein (w/w), which were heated to 90C for gel formation. Specific attention was focused on the temperature dependence of the mechanical properties of the gels during cooling and reheating. In all cases the magnitude of the complex modulus |G*| was found to increase with decreasing temperatures from 90 to 30C. The tan δ, which is related to the relative viscoelasticity of the gels, increased with decreasing temperatures from 90 to 60C. At temperatures between 60 and 30° C, tan δ remained constant. The dependence of |G*| and tan δ on temperature was found to remain constant during heating and cooling between 30 and 70C, indicating that rheological changes were reversible within this temperature range.     

Heat Transfer Study on Flame Pasteurization of Liquids in Aluminum Cans

Heat transfer studies were performed in 209 × 413 aluminum cans using 1% bentonite suspension. The cans were heated in a pilot flame sterilizer. The temperature profile was practically uniform radially and axially after 4.5 min of heating. The slowest heating was experienced in the bottom (heel) of these cans. The temperature difference between the slowest heating point and the hot region over the flame decreased as the can was heated: from 15.6°C after 1 min to 6.7°C after 4.5 min of heating. The internal heat transfer coefficient at 40 rpm was measured and showed an increase with heating time.     

Secondary adsorption of milk proteins from the continuous phase to the oil–water interface in dairy emulsions

Low protein surface concentration emulsions are susceptible to secondary protein adsorption where protein moves from the continuous phase to the existing, oil–water interface. The resulting increase in protein surface concentration can greatly alter emulsion properties. Butteroil was emulsified with whey proteins and the emulsion was combined with a solution of dissolved skim milk powder (SMP), producing mixes with fat and protein levels representative of ice cream. The primary adsorbed layer was modified by heating the whey protein solution prior to emulsion formation (70°C, 80°C, 90°C), by heating the emulsion (70°C, 80°C, 90°C) or by pH adjustment of the emulsion (6–8). Modifications of the SMP solution included heat treatment (80°C, 95°C) or sugar addition with or without κ-carrageenan. The effect of addition of SMP solution on the protein surface concentration and shear stability of the diluted emulsions was determined. Addition of untreated solution to the control, heated or pH adjusted emulsions greatly reduced shear destabilization and increased the protein surface concentration. Addition of heat treated or sugar containing SMP solution to the control emulsion produced the same result. However, sugar and carrageenan in the mix maintained the susceptibility to partial coalescence and reduced the secondary adsorption of caseins and whey proteins.     

Comparison of high pressure treatment and thermal pasteurization effects on the quality and shelf life of guava puree

The effects of high pressures and thermal pasteurization on the survival of microorganisms, enzyme inactivation and quality changes of guava puree during storage at 4°C were investigated and compared with untreated samples. After treatment at a pressure of 600MPa and 25°C for 15 min, the microorganisms in guava puree were inactivated to less than 10 cfu mL⁻¹ and the product exhibited no change in colour, pectin, cloud and ascorbic acid content as compared with fresh samples. The inactivation of enzymes in guava puree by thermal pasteurization was greater than by high pressures. The microbial count in guava puree reduced to 200 cfu mL⁻¹ and the product showed marked changes in viscosity, turbidity and colour when heated at 88–90°C for 24s. The content of pectin, cloud and ascorbic acid as well as colour in untreated and high pressurized (400MPa) guava puree gradually decreased, whereas these changes were not observed in pasteurized (88–90°C) and high pressurized (6000MPa) puree during storage at 4°C for 60 days. The guava puree treated at 600MPa and 25°C for 15 min retained good quality similar to the freshly extracted puree after storage at 4°C for 40 days.     

Assessment of the previous heat treatment given to meat products in the temperature range 40°–90°C. Part 1: Soluble nitrogen analysis

The aim of this work was to identify a technique which would yield information retrospectively about the heat treatment applied to a meat product in the temperature range 40–90°C. Saline extracts of beef samples ( M. longissimus dorsi and M. semi-membranosus ) of known heat treatment, were analysed for soluble nitrogen by Kjeldahl analysis. The amount of residual soluble nitrogen in an extract was found to decrease as the cooking temperature increased, with the major reduction occurring between 40 and 70°C. A good correlation between nitrogen values was obtained for aliquots removed from a continuously heated raw meat extract, 5 mm slices and the centre sections of 60 mm cubes. It was also possible to detect differences in the extent of heating achieved at points between the surface and the centre of the solid piece of meat. These results indicate that it may be possible to estimate in retrospect the approximate maximum temperature reached in an unknown cooked meat sample by reference to a standard curve of soluble nitrogen versus known heat treatment.     

Sardine Surimi Gels as Affected by Salt Concentration, Blending, Heat Treatment and Moisture

The effects of simultaneous modification of salt concentration, blending time, moisture content and heat treatment at different setting and cooking temperatures and time on characteristics of sardine (Surdina pilchardus) surimi gels was examined using a randomized incomplete block design. Maximum gel strength (GS) was obtained at highest salt concentrations and 78% moisture. Pre-setting was required to achieve acceptable gel quality. Highest GS values were found in gels set for 30–60 min at 35°C prior to heating at 90°C for 40 min. However, GS decreased after prolonged heating at 90°C. Gels set at 25, 35 and 40°C for 90 min had lower GS values when heated at 90°C for 40 min but were stable during further heating.