ABILITY OF VARIOUS CHEMICALS TO REDUCE COPPER AND TO INACTIVATE MUSHROOM TYROSINASE1

Treatment of mushroom tyrosinase with reducing agents such as hydrogen peroxide, ascorbic acid, phenylhydrazine, gallic acid, ferrocyanide and NH₂OH resulted in inactivation of the enzyme. Under the conditions tested, 50% inactivation of the enzyme was obtained with 4 μM H₂O₂, 20 μM ascorbic acid, 40μM phenylhydrazine, 6 mM gallic acid, 12 mM ferrocyanide and 22 mM NH₂OH. The ability of the reducing agents to reduce Cu²⁺ in a chemical model system was determined and it was found that gallic acid, phenylhydrazine, ascorbic acid and NH₂OH are relatively good reductants of Cu²⁺ while H₂O₂ and ferrocyanide are relatively poor ones. The copper content of mushroom tyrosinase before and after inactivation by each of the reducing agents was determined. The copper content of the enzyme inactivated by H₂O₂, NH₂OH, phenylhydrazine, ferrocyanide, gallic acid and ascorbic acid was 100%, 90%, 90%, 85%, 85% and 76% compared to that of the control (enzyme not treated). It was concluded that the degree of inactivation of mushroom tyrosinase by the reducing agents was not correlated with the decrease in the copper content of the enzyme nor with their ability to reduce Cu²⁺ in a chemical model system.     

EFFECTS OF CHITOOLIGOSACCHARIDE ON THE PHYSICOCHEMICAL, TEXTURAL AND SENSORY PROPERTIES OF TOFU

Chitinous polymers have been experimented with for the purpose of shelf-life extension of foods due to their antimicrobial activity. Food additives, however, may impair the taste, color or texture of foods. Therefore, it is necessary to evaluate the effect of a food additive on foods before it is used. In this study, we investigated how the physicochemical properties, microstructure, textural properties and sensory characteristics of tofu are affected by the addition of chitooligosaccharide during its preparation. The addition of chitooligosaccharide to tofu did not significantly affect its physicochemical properties including moisture content, yield, turbidity and color. The chitooligosaccharide tofu, however, had lower hardness and smaller protein aggregates than the control tofu. The chitooligosaccharide did not influence most sensory attributes of tofu except for imparting a bitter taste.     

EFFECTS OF INULIN AND BULKING AGENTS ON SOME PHYSICOCHEMICAL, TEXTURAL AND SENSORY PROPERTIES OF MILK CHOCOLATE

Chocolates are favorite foodstuffs with high sugar contents. Therefore, in the present study, the production of a low-sugar milk chocolate with prebiotic properties is evaluated. Various ratios of inulin (IN), polydextrose (PD) and maltodextrin (MD) along with sucralose (0.04% w/w) were used instead of sugar. Fifteen formulations were examined to determine some physicochemical, mechanical and sensory properties in order to find their optimum ratios. In general, formulations with high ratios of PD and MD were moister and softer than control. The lowest moisture content and highest hardness were observed for the moderate ratios. In addition, MD induced the least desirable sensorial effects, whereas PD and IN pronouncedly improved the overall acceptability. The optimum applicable range for IN, PD and MD were 14–32% and 71–84%, 7–26% and 67–77%, and 0–20% of sugar substitutes, respectively. Our findings on simultaneous fat and sugar reductions also indicated the possibility of fat cut up to 5% in comparison to previous fat content.

PRACTICAL APPLICATIONS

In this paper, we have reported the influences of inulin (IN) as a prebiotic as well as polydextrose (PD) and maltodextrin (MD) as bulking agents on physicochemical, energy content, texture and sensory properties of milk chocolate using simplex lattice mixture design. To the best of our knowledge, this is the first report in this field with very interesting results and practical applicability. Moreover, our findings showed that the use of aforementioned ingredients instead of sugar could lead to production of low-calorie milk chocolate without having the undesirable textural and physiological effects on the product and consumers. Moreover, the simplex lattice mixture design was found a very useful technique for finding optimum ratios of sugar replacers in formulation.     

EFFECT OF RAPID COOLING ON THE GROWTH AND PENETRATION OF SALMONELLA ENTERITIDIS INTO EGG CONTENTS

Shell eggs were inoculated internally with approximately 10 cells of Salmonella enterica serovar enteritidis (S. enteritidis) and subjected to three different cooling treatments. Eggs were cooled from an initial temperature of 27C to approximately 7.2C. After cooling, eggs were stored at approximately 7.2C for 36 days, or stored at 5.7–9.5C for 30 days plus 6 days at 37C to simulate temperature abuse. Rapid cooling and subsequent storage of eggs at approximately 7.2C inhibited the growth of S. enteritidis in eggs. Slow cooling, and/or temperature abuse promoted growth of S. enteritidis in eggs. The penetration study indicated that rapid cooling and subsequent storage at 7.2C for 30 days did not affect the penetration of S. enteritidis into egg contents. The S. enteritidis isolated from the eggshell with shell membranes was significantly higher (P < 0.05) than from the internal egg contents, indicating that most of the S. enteritidis cells were trapped within the shell pores and/or shell membranes.     

SODIUM LACTATE EFFECTS ON MICROBIAL, SENSORY, AND PHYSICAL CHARACTERISTICS OF VACUUM-PACKAGED PORK SAUSAGE

Vacuum-packaged fresh meat products held at refrigeration temperatures have limited shelf-life expectancies, often due to growth of anaerobic lactic acid-producing bacteria. Agents that can suppress the growth of this group are beneficial. Fresh pork sausage, formulated to contain 0%, 1%, 2%, or 3% sodium lactate (SL), was vacuum packaged and stored at 4C for 0, 10, 17, 24, and 31 days. A trained sensory panel evaluated pork, salty, sour, and bitter flavors. Aerobic total plate counts (APC), anaerobic total plate counts (AnPC), aerobic lactic acid producers (ALC), anaerobic lactic acid producers (AnLC), TBA values, and pH were determined. SL depressed APC, AnPC, and AnLC. Addition of 1% SL extended shelf-life of vacuum-packaged fresh pork sausage by 1 week compared to controls; samples containing 2% and 3% SL had not reached spoilage level (log₁₀ 7.0 CFU/g) at the conclusion of this study. Addition of SL increased salty taste and prevented loss of pork flavor over time, but had no effect on sour or bitter flavors.