EFFECT OF PRESSURE AND STORAGE TIME ON TEXTURE PROFILE PARAMETERS OF SOYBEAN CURD (TOFU)

The pressure applied to soybean curd during processing into tofu has a profound effect on the moisture content, yield and some textural parameters of tofu. As the pressure increased from 0.186P to 0.744 P the moisture content decreased from 82% to 60% and yield decreased from 2.0 kg to 1.2 kg per kg whole dry soybeans. Hardness-1, hardness-2, chewiness andgumminess increased linearly with increasing pressure. Springiness, cohesiveness, adhesiveness and stringiness were hardly affected by increasing pressure. During storage in water at 2–3°C for 3 weeks, hardness, gumminess, and adhesiveness increased moderately; springiness decreased moderately and the other texture parameters were almost unchanged.     

ETHANOL ACCUMULATIONS IN MUSCLE TISSUE AS A CHEMICAL INDICATOR OF FISH SPOILAGE

Ethanol concentration was shown to accumulate in post mortem muscle tissue of marine fish as storage time increased. Concentration of the alcohol was determined using a rapid, enzymatic procedure. A study was conducted under commercially simulated storage conditions comparing the effectiveness of ethanol in monitoring fish spoilage to three more common quality tests. The ethanol method mas shown to be as effective as established organoleptic, chemical, and biological testing procedures when following fish flesh degradation.     

DETECTION OF BIOGENIC AMINES AS MEAT SPOILAGE INDICATORS

Preparative ion exchange chromatography was performed on beef and pork samples stored at 4–6°C and wrapped in commercial film (Saran). Different peaks obtained for the two species studied, were attributable to the different type of biogenic diamines produced during spoilage. A second set of experiments was performed with pork, beef and rabbit samples. The last served as a control, since no record was available for the time elapsed since slaughtering of the animals of the other two species. Analyses were performed to determine total amine nitrogen produced during storage at chill temperatures in wrapped and unwrapped samples, and the amount of Pseudomonas , total aerobic organisms and lactic acid bacteria. Results suggested that the wrapping material did not produce the microaerophilic conditions to promote the growth of required lactic acid bacteria sufficient to outnumber the other microorganisms present. However, diamine production was slower in wrapped than in unwrapped samples.     

EFFECT OF SOYBEAN STORAGE ON TOFU AND SOYMILK PRODUCTION1

Century 84 and Century -L₂L₃ (lacking lipoxygenase isozymes 2 and 3) near isogenic soybean varieties were stored at five temperature and relative humidity conditions for up to three months. At one-month intervals, soybeans were retrieved from storage and processed into soymilk and tofu. Chemical and physical characteristics of the soybeans, soymilk, and tofu were analyzed. In general, soybean storage above 25C and 50% relative humidity adversely affected the characteristics of the soymilk (reduced pH and solids content) and tofu (decreased yield and moisture content, and darker color) produced. Century -L₂L₃ soybeans were more resistant to changes during adverse storage than were Century 84 soybeans.     

SOYMILK VISCOSITY AS INFLUENCED BY HEATING METHODS AND SOYBEAN VARIETIES

In the two‐step heating experiments, soymilk with 5% protein was first heated at 55, 60, 65, 70, 75 or 80C for 10 min, and then heated at 97C for another 10 min. As a control, the soymilk was heated at 97C for 10 to 60 min by continuous one‐step heating. The viscosity of the heated soymilk was measured after cooling to room temperature. Results showed that the two‐step heating increased the soymilk viscosity by up to six times the viscosity of the control. The maximal viscosity was reached when the first‐step heating temperature was 70C. Differential scanning calorimetry showed separate denaturation of soy 7S and 11S proteins was related to the viscosity increase. Soymilk protein content and soybean variety also influenced the viscosity. Three heat transfer methods, including ohmic heating, steam injection and water bath heating, produced different viscosities of soymilk.     

PHYSICOCHEMICAL CHARACTERISTICS OF SOFT TOFU FORMULATED FROM SELECTED SOYBEAN VARIETIES1

Currently, hundreds of soybean varieties with a wide range of quality attributes are available. The majority of these soybean varieties have not been evaluated for their quality in soymilk and tofu. In this research, tofu was prepared using the hot ground method by coagulating soymilk from four soybean varieties (Macon, Saturn, OHIOFG1 and OHIOFG2) with calcium sulfate dihydrate. Soybean variety significantly affected yield, held water, color parameters, viscosity, storage modulus, and textural properties of tofu cakes. Soymilk with higher pH, viscosity, and protein produced tofu with higher protein, water held, and yield. Varietal differences should be considered in selecting soybeans for tofu production. Macon soybeans produced the best tofu with regards to quality attributes.     

EFFECTS OF ESCULETIN AS A LIPOXYGENASE INHIBITOR IN SOYBEAN EXTRACTS

This study was designed to determine the ability of esculetin to inhibit lipoxygenase activity in soybean. Lipoxygenase was extracted from ground soybean using 0.1 M Tris-HCl buffer (pH 8.6) and centrifuged at 3000 g for 15 min at 4C. The extract was mixed with different volumes of 0.05M esculetin solutions to provide 1.8 × 10⁻⁴M, 3.3 × 10⁻⁴M, 4.6 × 10⁻⁴M and 5.7 × 10⁻⁴M to final assay systems, respectively. Lipoxygenase activity decreased as the concentration of esculetin solution mixed in soybean extract increased. Mixing of 1.8 × 10⁻⁴M esculetin solution to soybean extract showed the least inhibition effect and was significantly different from that of 3.3 × 10⁻⁴M, 4.6 × 10⁻⁴M and 5.7 × 10⁻⁴M which inhibited LOX (lipoxygenase)'s activity of soybean extracts. In the study comparing the inhibition abilities for lipoxygenase activity among selected antioxidants, esculetin was significantly better than BHA (butylated hydroxyanisole) and α-tocopherol.     

STUDIES OF RETARDING AGENT FOR DECREASING STARCH RETROGRADATION IN WANKAO (RICE CURD)

ABSTRACT

WanKao (rice curd) products, included control and added pregelatinized waxy rice flour (PWRF) retarding agent, were prepared and evaluated by texture profile analysis and sensory evaluation. The results showed that the amylose complexing index of the WanKao products contained PWRF were higher than the control, and directly added α‐amylase or monoglycerides. Upon storage, WanKao products contained PWRF showed higher water activity and starch digestibility than those added α‐amylase or monoglycerides. The hardness and soluble starch content of WanKao products contained PWRF were significant lower than those of added α‐amylase or monoglycerides and the control. The WanKao products added PWRF also exhibited softer texture during storage. For sensory evaluation, the higher score of was the added PWRF‐D (contains 100 g of waxy rice flour, 200 g of water, 6% of monoglycerides and 400 mg/kg of α‐amylase) WanKao product presented higher overall acceptability than that of added α‐amylase, monoglycerides, and control either fresh or after low‐temperature storage (5C for 5 days). As a result, the texture qualities of WanKao could be improved by the addition of the PWRF and also the staling and retrogradation rates were further retarded.

PRACTICAL APPLICATIONS

Taiwan's consumers demand for high quality WanKao products, i.e., softer, slow to staling and retrogradation, and good acceptability. Our results indicated that the qualities of WanKao could be improved by the addition of the novel retarding agent, PWRF, and the staling and retrogradation rates were further retarded.     

水豆腐保鲜技术的研究讲展

阐述了多种杀菌技术与保鲜技术在豆腐保鲜研究中所取得的成果,分析了豆腐保鲜难的部分原因,并展望了水豆腐保鲜技术的发展方向.     

PHYSIOLOGICAL ACTIVITIES OF CHUNGKOOKJANG (KOREAN TRADITIONAL SOYBEAN PASTE) PILL AS A FUNCTIONAL FOOD

Chungkookjang, Chungkookjang pill and mushroom (Lentinus edodes) had fibrinolytic activities. The mushroom had a higher level of fibrinolytic activity (15.1 unit/mg) than Chungkookjang pill (10.0 unit/mg) and Chungkookjang (0.6 unit/mg) in spite of heat treatment. Hot‐water extracts of Chungkookjang and Chungkookjang pill showed slightly higher macrophage‐stimulating activities than the positive control, lipopolysaccharide. Also, Chungkookjang pill (3.58 µg/g) had lower cyclo‐His‐Pro content than Chungkookjang (26.5 µg/g). In addition, Chungkookjang pill had less content of flavor components than Chungkookjang and, especially, the 2,5‐dimethylpyrazine content of Chungkookjang pill was less than that of Chungkookjang. When comparing with Chungkookjang, Chungkookjang pill had similar physiological activities and more palatable flavor.     

IDENTIFICATION AND CHARACTERIZATION OF THE MICROFLORA AND SPOILAGE BACTERIA IN FRESHWATER CRAYFISH Procambarus clarkii (Girard)

Crayfish tails were collected from two commercial peeling plants in South Louisiana and stored at 0° and 5°C. Initially and after various periods of storage, bacteria were isolated from the peeled tails, identified generically and subsequently classified on the basis of their ability to produce "spoilage" in sterile crayfish tail flesh. Micrococcus, Staphylococcus, Alcaligenes and Achromobacter were the predominant genera in the fresh samples of tails. Achromobacter predominated during early storage and Pseudomonas and Achromobacter were the dominating organisms in the spoiled tails. Of the 280 isolated bacteria, 22.1% were classified as "rapid spoilers," 16.4% were "slow spoilers" and 61.5% were "nonspoilers." Most of the spoilers were Pseudomonas , while an appreciable number belonged to Achromobacter.