Purification and Characterization of a Pregastric Esterase From a Hygienized Kid Rennet Paste

Relevant pH and lipase for in vitro models of gastric digestion

The development of in vitro digestion models relies on the availability of in vivo data such as digestive enzyme levels and pH values recorded in the course of meal digestion. The variations of these parameters along the GI tract are important for designing dynamic digestion models but also static models for which the choice of representative conditions of the gastric and intestinal conditions is critical. Simulating gastric digestion with a static model and a single set of parameters is particularly challenging because the variations in pH and enzyme concentration occurring in the stomach are much broader than those occurring in the small intestine. A review of the literature on this topic reveals that most models of gastric digestion use very low pH values that are not representative of the fed conditions. This is illustrated here by showing the variations in gastric pH as a function of meal gastric emptying instead of time. This representation highlights those pH values that are the most relevant for testing meal digestion in the stomach. Gastric lipolysis is still largely ignored or is performed with microbial lipases. In vivo data on gastric lipase and lipolysis have however been collected in humans and dogs during test meals. The biochemical characterization of gastric lipase has shown that this enzyme is rather unique among lipases: (i) stability and activity in the pH range 2 to 7 with an optimum at pH 4-5.4; (ii) high tensioactivity that allows resistance to bile salts and penetration into phospholipid layers covering TAG droplets; (iii) sn-3 stereospecificity for TAG hydrolysis; and (iv) resistance to pepsin. Most of these properties have been known for more than two decades and should provide a rational basis for the replacement of gastric lipase by other lipases when gastric lipase is not available.

Influence of diet and rennet on the composition of goats’ milk and cheese

Dry matter, protein, fat, pH, mineral (Na, K, Ca and Mg) and trace elements (Fe, Cu, Zn and Se) concentrations were determined in samples of goats’ milk and in fresh, semi-hard and hard cheeses to study the effect of the goats’ diet and the type of rennet used for the cheese processing of the Palmero Protected Designation of Origin cheeses. Two groups of 20 Palmero goats were fed 2 different diets: a Palmero diet (PD supplied by native forages adapted to subhumid areas, which had a high ratio of long fibre to concentrates (65:35), and an actual diet (AD), the most commonly used by goat farmers, with a low ratio of long fibre to concentrates (35:65). In general, the cheese samples from goats fed with PD had higher mean Ca, Zn, Cu and Se concentrations than the samples obtained from AD fed goats. The diet exhibited a greater influence on the chemical composition of the cheeses than the rennet used in their production. Applying a stepwise linear discriminant analysis a complete percentage of correct classifications of the three types of cheeses according to the diet of the goats was observed.

Hygienic quality of ewes' milk cheeses manufactured with artisan-produced lamb rennet pastes

The use of artisan-produced lamb rennet pastes, but not any of the other commercial animal rennets, imparts a characteristic flavour to the cheese, so most Mediterranean ewes' milk cheeses are coagulated with this kind of rennet paste. In contrast to the advantages of using lamb or kid rennet pastes from the sensory point of view, questions are still raised as to their hygienic quality. The goal was to examine the microbiological and enzymic quality of lamb rennet pastes prepared by cheese manufacturers for their own use, and evaluate the hygienic quality of raw sheeps' milk cheeses made with them, using Idiazabal cheese as a model. Lamb rennet pastes prepared by artisan cheese makers from the Basque region of Spain (27), and Italy (8) were evaluated. For cheese making experiments 5 different lamb rennet pastes were selected among the 27 samples from the Basque Country region of Spain. Microbiological analyses were carried out on samples from rennet pastes, rennet extracts, milks and cheeses during ripening. Enzymic activities studied in rennet paste were: total coagulating strength and lipase. Analysis of variance and Student's t-tests was performed. The results show that the artisan-produced rennet pastes contain high levels of a variety of microorganisms. After 60 ripening days, which is the minimum ripening period required for Idiazabal cheese prior to its commercialization, no Eschericia coli, Clostridium, Salmonella spp. or Listeria monocytogenes were detected, and levels for the rest of the microorganisms were below the limits of the European legislative standards for cheese manufactured with raw milk. We can conclude that the use of artisan-produced lamb rennet pastes of questionable hygienic quality for the manufacture of raw milk hard cheeses yields products of good hygienic quality.