Review: Studies on the reproductive and developmental biology of <I>Cichlasoma dimerus</I> (Percifomes,Cichlidae)

Many characteristics of the South American teleost fish Cichlasoma dimerus (body size, easy breeding, undemanding maintenance) make it amenable to laboratory studies. In the last years, many of the fundamental aspects of its reproductive and developmental biology have been addressed in our laboratory. Rather recently, the immunohistochemical localization of pituitary hormones involved in reproduction and in background color adaptation has been described in both adult and developing individuals, and the role of FSH in ovarian differentiation has been established. These findings have been correlated with mapping of some of their brain-derived controlling hormones. The latter include brain-derived gonadotropins which were shown to be active in vitro in the control of pituitary hormone secretions. The emerging picture shows C. dimerus as an interesting species in which many of their basic features have already been investigated and which conform a solid platform for comparative studies correlating neurohormones, pituitary hormones and behavior, from the molecular to the organismic level.     

Effects of Food Gums on Zinc and Iron Solubility following in vitro Digestion

The effects of three levels (0.1, 0.3 and 0.5%) of locust bean gum, guar gum and sodium alginate on zinc and iron availability were evaluated in milk and soy systems. Availability was estimated as metal solubility after digestion with pepsin-HCl followed by addition of bicarbonate and digestion with pancreatic and bile extracts. Locust bean gum (0.5%) and guar gum (0.5%) reduced zinc solubility by 23.5 and 69.6%, respectively, in the milk and by 41.1 and 40.1% in the soy. Smaller reductions were observed at lower gum levels. The two gums also caused significant reductions in iron solubility from soy. Sodium alginate exerted little effect on mineral solubility.     

Computer-Based Retort Control Logic for On-Line Correction of Process Deviations

A control logic algorithm is described for use with computer-based control systems on batch retort operations in the thermal processing of canned foods. The system is capable of automatically adjusting process time during the cook cycle to compensate precisely for any unexpected deviation in retort temperature. It takes into account the cooling lethality contributed with conduction-heating foods, and does not rely on any test cans for monitoring product center temperature. Performance is demonstrated by computer-generated plots showing actual retort temperature history along with calculated center temperature and accumulated process lethality; and results are compared with other methods.     

VIABILITY OF BIFIDOBACTERIUM LA CTIS AND LACTOBACILL US ACIDOPHILUS IN MILK: SODIUM CHLORIDE CONCENTRATION AND STORAGE TEMPERATURE

The growth and viability of Bifidobacterium lactis and Lactobacillus acidophilus per se and for both strains as a coculture were studied in reconstituted skim milk so as to assess their dependence upon temperature (5, I0 and 15C), NaCl concentration (0, 0.51 and 1.03 mol L-'), and storage time (0–8 weeks). Cultures of B. lads exhibited no signijkant loss of viability either with increasing NaCl concentration or increasing storage temperature within the ranges studied On the other hand, viability of L. acidophilus decreased with increasing temperature and increasing NaCl concentration under similar conditions. When cocultured with L. acidophilus, B. lactis was signiJicantly less tolerant to higher NaCl levels and higher temperatures than when in pure culture, although rial numbers were still above the threshold required for commercial application. Coculturing with B. lactis had no detrimental effect on viability of L. acidophilus. A mechanistic model, which considers the behavior of the pure and mixed microbial populations is described by specijic death rates which vary with temperature following Arrhenius relationships) and NaCl levels following simple inhibition kinetics) in the milk medium. Activation energies for the death rates of B. lactis and L. acidophilus were 14 kcal mot' and 9–15 kcal mol-I, respectively.     

Oxygen Uptake and ß-Carotene Decoloration in a Dehydrated Food Model

Oxygen uptake of a model system containing β-carotene was measured by a method capable of determining headspace oxygen and entrapped oxygen, both at low concentrations. β-Carotene was determined colorimetrically at 460 nm. A first-order mechanism was found for this reaction with respect to β-carotene concentration as measured by color. The values of the rate constants were functions of the oxygen concentrations in the headspace of samples; they increased as these concentrations increased. Up to seven molecules of oxygen were consumed as each molecule of β-carotene was discolored. This high oxygen consumption was not related to the oxidized products. A mathematical model was developed, based on the experimental data, to predict β-carotene decoloration by measuring oxygen uptake or to determine oxygen uptake from decoloration. A computer program was developed to make these predictions. Samples with known histories had linear correlations between oxygen uptake and β-carotene decoloration. The results for 1% and 2% headspace oxygen concentrations agreed with experimental values, presenting a standard deviation compatible with the experimental methods used. An important corollary is the suitability of a simple colorimetric test for monitoring oxygen uptake in a dehydrated system.     

OPTIMIZATION CRITERIA FOR BATCH RETORT BATTERY DESIGN AND OPERATION IN FOOD CANNING-PLANTS

Optimization of thermal processing in the commercial sterilization of canned foods is of great interest because the canning industry plays an important role within the economy of the food processing sector. Many food canning plants operate in a batch mode with a battery of individual batch retorts. The aim of this study was to propose and analyze several criteria and methodologies for optimum design and operation of such retort systems. Two criteria were proposed in the case of choosing the optimum number of retorts to be installed when designing a new batch‐operated canning line. The third criterion dealt with seeking optimum process conditions for maximizing output from a fixed number of retorts when processing small batches of different products and container sizes. In the case of new plant design optimization, one objective was to determine the optimum number of retorts that would minimize on‐going processing costs related to labor and energy. Retort scheduling (programming) was studied from which a simple mathematical expression was derived for this purpose. A second objective was to determine the optimum number of retorts that would maximize the net present value of initial investment. Approaches based upon engineering economics were studied from which to develop a mathematical procedure for this purpose. In the case of maximizing output from a fixed number of retorts for different products and container sizes, isolethal processes were identified for various product/containers from which a common set of process conditions could be chosen for simultaneous processing of different product lots in the same retort.     

Explicit Finite Difference Methods for Heat Transfer Simulation and Thermal Process Design

A considerable difference between two explicit finite difference heat transfer simulation approaches was described. Time step restrictions, which are often the basis for criticism of explicit methods, were shown to be less severe when the surface was not considered to have thermal mass. Thermal process design combines heat transfer and reaction kinetics considerations. Accuracy of lethality estimates depends on time step size. Guidelines were developed for applying discrete time-temperature data to thermal process calculations. For time steps small enough to permit a linear temperature change approximation, it was shown that for increasing (decreasing) temperatures, a value within 50 to 60% (40 to 50%) of total temperature change should be used.