Food Science and Technology International

Edible tissues of food animals may contain residues of chemical substances harmful to human health, including animal drugs, mycotoxins and environmental contaminants. Current meat inspec tion activities rely mainly on visual inspection of the carcass and its offals at the slaughterhouse, and fail to detect chemical residues and enteric pathogens that are considered as major health risks associated with meat consumption. In contrast to traditional approaches, application of the hazard analysis critical control point (HACCP) to meat production and inspection, constitutes the best alternative to reduce the incidence of residues and to improve meat safety. Application of HACCP to meat inspection virtually eliminates the need for finished product testing by identi fying the safety risks inherent in the meat production steps, from farm to table, and devising preventive measures which can be monitored in order to control the process. Accordingly, there is also a need for the development and application of analytical methods of enough sensitivity that allow real-time monitoring of chemical residues in live animals and their tissues.

The effect of system composition on sorbate destruction and sensory damage due to non-enzy matic browning was studied in aqueous model systems with a water activity (a _w) of 0.91 and a pH of 5.0-6.0. The rate constants of sorbate destruction could be described by first order kinetics and those from non-enzymatic browning by zero order kinetics. Both reactions were found to be related not only to temperature and pH but also to the humectants (NaCl, glycerol) used to depress a _w. A higher preservative retention and a smaller amount of browning was produced by the use of a mixture of 35.0 g/kg of NaCl and 220.0 g/kg of glycerol as a humectant instead of one of them alone, citric acid instead of phosphoric acid as the acidifying agent, and glass flasks instead of polyethylene containers. The non-enzymatic browning reactions were greatly influenced by sorbic acid destruction. The inclusion of glycine was responsible for the enhanced sorbate destruc tion and browning development.

The dynamics of a twin screw food extrusion process, including product quality attributes (PQA), to change in feed rate, water rate, screw speed, and barrel temperature at zone 5 were defined. Two PQA variables clearly dominated, colour-b and collet moisture content, which were highly correlated to bulk density. Product temperature at the die also showed high steady-state correla tion with bulk density. Moisture in the barrel was the primary driver for the colour-b and collet moisture content responses. Barrel temperature-5 was important in the response of product temper ature, but excessive delay times made it less important as a control variable. The gains indicated a non-linear system over the response range explored.

Abraded (up to 20%) ground naked non-waxy and waxy barleys were blended with wheat flours. Amylograph peak temperatures of wheat/barley blends (85:15) decreased by 1.5 °C with non- waxy barley and by 3.5 °C with waxy barley. Peak viscosities of wheat flours was increased by the addition of non-waxy barley and decreased by the addition of waxy barley. Adding either non-waxy or waxy barley increased breakdown viscosities. Texture profile analysis (TPA) para meters of udon noodles prepared from wheat-barley blends were largely unaffected by non-waxy barley, but were lowered by waxy barley and by potato, corn or barley starches. Whereas incor poration of increasingly abraded non-waxy barley had little effect on the TPA parameters of udon noodles, addition of increasingly abraded waxy barley decreased hardness and chewiness of udon noodles. A shorter cooking time is required to cook noodles from wheat-barley blends (as indicated by lower peak viscosity temperatures and more open internal structures of noodles, as seen by scanning electron microscopy) than from wheat flour. Extent of colour darkening of udon noodles was reduced as the added barley flours were obtained from increasingly abraded grain.

Aerobic fermentation of cheese whey by Kluyveromyces fragilis has been proposed as a means of reducing its pollution potential and of producing ribonucleotide derivatives. 5'-Ribonucleotides, such as 5'-GMP and 5'-IMP are high added-value products that are used as flavour enhancers in foods. 5'-Ribonucleotide derivatives, nucleosides, nucleoside analogues and free bases are known to have anti-tumour, anti-viral and probiotic effects. In this study, K. fragilis was grown in a medium containing dehydrated whey under aeration. After different times of fermentation (24, 48, 72 h) aliquots of cells were autolysed either by incubation at three different fixed temperatures (48, 50, 53 °C) for 48 h or by incubation through a temperature gradient (45-65 °C, increasing by 5 °C every 5 h). Autolysed cells were centrifuged and the supernatant was analysed by high perfor mance liquid chromatograpy. High concentrations of free bases (0.74%) and 3'-nucleotides (0.64%) on the basis of biomass (d.w.) were obtained by a specified autolysis condition (50 °C, pH 7.5, 48 h), but less than 0.1% of 5'-nucleotides were obtained. Autolytic enzymes were able to break the yeast cells and hydrolyse the molecules of RNA into compounds that have therapeutic effects (free bases), but were not able to transform them into 5'-GMP and 5'-IMP.

Evolution of the whey proteins fractions and proteolysis indices from 12 batches of the artisan cheese Afuega'l Pitu variety were studied by reversed phase high performance liquid chro matography (RP-HPLC) over the ripening period. The correlation coefficients between the whey protein contents and ripening time were very low, indicating that the whey protein content did not change as the cheese aged. However, soluble nitrogen content and the percentage of total nitrogen in the soluble form showed correlation coefficients higher than 0.9 with increasing ripening time. Analysis of variance showed significant differences (p < 0.05) between dairies for most of the variables with the exception of β-lactoglobulin A and bovine serum albumin. These variables were also significantly different between the two manufacture zones. Conversely, no significant differences (p < 0.05) were observed between the two varieties of cheese, red and white, for whey protein content or for proteolysis indices.

Mixtures of 0, 10, 20, 30 or 40% chicken thigh meat with potato flakes were adjusted to 21% mois ture content and extruded. A Brabender single screw extruder was used with zones 1 and 2 at 110 °C, zones 3 and 4 at 130 °C and zone 5 at 150 °C, feed rate 900 g/min and screw speed 60 rpm. Extrudates were then baked at 121 °C to a final moisture content of approximately 5%. As the meat content increased, fat and protein contents increased and shear force and expansion decreased. Air cell size and number decreased and extrudates appeared sponge-like at 0, 10 and 20% chicken and as a continuous protein-carbohydrate structure at 30 and 40% chicken. Total aerobes, yeasts and moulds were less than 11 cfu/g of extrudate.

The aim of this work was to elaborate a predictive model of the mass transfer (water loss and solute gain) that occurs during dewatering and soaking by using neural network modelling. Two separate feedforward networks with one hidden layer were used (for water loss and solute gain respectively). Model validation was carried out on results obtained previously, which dealt with agar gel soaked in sucrose solution over a wide experimental range (temperature, 30-70 °C; solu tion concentration, 30-70 g sucrose/100 g solution; time 0-500 min; agar concentration, 2-8%). The best results were obtained with three hidden neurons, which made it possible to predict mass transfer, with an accuracy at least as good as the experimental error, over the whole experimental range. The technological interest of such a model is related to a rapidity in simulation compa rable to that of a traditional transfer function, a limited number of parameters and experimental data, and the fact that no preliminary assumption on the underlying mechanisms was needed.