Changes in gastric resistance of Lactobacillus casei in flavoured commercial fermented milks during refrigerated storage

This study investigated the gastric acid resistance ofLactobacillus caseiin commercial fermented milks during refrigerated storage. Samples of fermented milks (natural, strawberry, fruits of the forest, vanilla and multifruits) were obtained from three different manufacturers. In vitro gastric acid resistance (GAR) was assessed in samples upon arrival to the laboratory and after 10 and 20 days of refrigerated storage at 5 °C and 12 °C. The GAR ofL. caseiin fermented milks may increase or decrease during storage in relation to the flavour and storage conditions. The occurrence of this phenomenon in commercial fermented milks containing probiotic bacteria may induce changes in their functionality after consumption.     

Textural Characteristics of Beef: Effects of the Heating System

Textural characteristics of beef semitendinosus roasts heated in 93 and 149°C ovens to 60 and 70°C were compared with those of small samples of semitendinosus heated as cylindrical cores in glass tubes in a water bath. The small samples were heated to the same endpoint temperatures as the roasts were at rates comparable to heating at the two oven temperatures. Cooking losses varied with heating method and in some cases with endpoint temperature and rate of heating. Heating method did not affect the textural parameters of penetration hardness, cohesiveness, and chewiness and shear cohesiveness and firmness. Hydroxyproline solubilization was greater in water bath samples than in intact samples heated at the slower rate. The extent of heat-related changes and their effects on final meat quality partially is determined by the heating system.     

Effects of Heating System, Temperature and Rate of Heating on Sensory Characteristics of Beef

Sensory scores for appearance and texture of oven-roasted beef semitendinosus were compared with those of samples heated in glass tubes in a water bath. Roasts heated in 93 and 149°C ovens appeared to be less done and were moister than water bath samples heated at comparable rates. Samples heated to 60°C in both systems appeared to be less done and were moister and less mealy than samples heated to 70°C. Few differences in sensory scores for textural parameters were attributed to heating system, endpoint or heating rate. Correlations between scores for intact roasts and objective measurements for the small samples were not always of the same direction or strength as were the relationships between scores and objective values for roast samples.     

INHIBITION OF ASPERGILLUS GROWTH AND EXTRACELLULAR AFLATOXIN ACCUMULATION BY SORBIC ACID AND DERIVATIVES OF FATTY ACIDS

A study was conducted to determine the effects of sorbic acid and several derivatives of fatty acids (amides, aminimides, and monoglycerides) upon toxigenic cultures of Aspergillus flavus and A. parasiticus. A synthetic medium was inoculated with spores, incubated for 48 h at 27°C, and then supplemented with sorbic acid and fatty acid derivatives. Cultures were then incubated for an additional 5 days. Aflatoxins were extracted, separated, and quantitated. Mycelial mats were dried, weighed, and analyzed for lipid and mineral content. Cerulenin (8 μg/ml) was the most effective fatty acid derivative examined, reducing mycelial growth by 37% and completely inhibiting extracellular accumulation of aflatoxins. Other derivatives, in decreasing order of effectiveness, included M-20 (an aminimide), lauribic, and lauricidin. Mycelia grown in the presence of fatty acid derivatives contained less phosphorus, potassium, magnesium, phosphatidyl ethanolamine, phosphatidyl serine, cholesterol, and triglycerides, but more cardiolipin, phosphatidyl choline, free fatty acids, fatty acid esters, and diglycerides. Levels of monoglycerides and cholesterol esters remained essentially unchanged. Inhibition by sorbic acid was nonspecific, affecting both mycelial growth and extracellular aflatoxin accumulation to approximately the same extent. Utilization of fatty acid derivatives for determining mechanisms of aflatoxin accumulation and lipid biosynthesis appears promising.     

LIPID-AUTOXIDATION-LIMITED SHELF-LIFE OF NIXTAMALIZED INSTANT CORN MASA

Consumers often report the presence of off-flavors and off-odors characteristic of lipid oxidation in commercial dry instant corn masa, but the extent of this problem is unknown. The lipid oxidation states of two common brands of nixtamalized instant corn masa produced in Mexico were evaluated during 23-weeks of storage at 15, 25, 35, 45, and 55C. Lipid autoxidation was evaluated by determining peroxide values (PV) and conjugated dienoic acids (CD) of extracted lipids, and sensory analyses of flours and tortillas made from stored flours. Increased storage time significantly increased lipid oxidation (P < 0.001). Similarly, increased storage temperature significantly decreased the time to reach rancid flavor thresholds. The Q₁₀ values for flours and tortillas were 1.58 and 1.75, respectively. The shelf-lives of instant corn masa were 5.8 months when stored at 25C and only 2 months at 45C.     

Effects of Sodium Tripolyphosphate on Physical and Sensory Properties of Beef and Pork Roasts

Six paired beef round and pork loin roasts were used to determine the effects of sodium tripolyphosphate (STPP) on fresh and reheated roasts. Roasts were pumped 10% of their weight with distilled water (control) or with distilled water containing 4.75% STPP. Roasts were cooked to internal temperatures of 70°C (beef) or 75°C (pork) and evaluated after 0, 1 or 3 days (roasts were reheated to cooked temperatures). This study indicates that phosphate in pork and beef roasts allowed them to be reheated after 1 and 3 days of refrigeration with minimal losses of juiciness, tenderness or flavor intensity, Phosphate injection reduced warmed-over flavor in reheated pork roasts but was not successful in decreasing the incidence of warmedover flavors in reheated beef roasts.     

Effect of Institutional Heating Methods of Cold and Hot Boned Restructured Beef Roasts

Hot- and cold-boned (HB and CB, respectively) restructured beef roasts were cooked in either: a conduction oven, convection steamer, low temperature cook/hold over or low temperature controlled humidity cook/hold oven. CB roast cooked in the conduction oven had higher cooking yields and lower shear values than CB roasts prepared by convection and low temperature controlled humidity cook/hold oven. HB roasts, cooked in the conduction oven, also had slightly higher cooking yields than other methods. No differences for shear values were apparent for HB roasts cooked in the various ovens. A sensory panel indicated CB and HB roasts had a browned beefy flavor, were juicy and moderately blended with little aftertaste. Restructured roasts are satisfactory for food service/institutional use but differences in yield and tenderness due to cooking method should be recognized.