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.

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A new cellulolytic Clostridium species that was isolated from decayed grass is described. The colonies produced by this organism on cellulose agar are circular, translucent, and unpigmented and have undulate margins. The cells of this bacterium are gram-positive straight to slightly curved rods 3 to 6 km long by 0.6 to 1 pm wide and are motile; they form round, terminal spores 1.5 pm in diameter. A variety of carbohydrates are fermented by this mesophilic anaerobe. The major fermentation products from cellulose are carbon dioxide, hydrogen, ethanol, acetate, lactate, and formate. The deoxyribonucleic acid base composition is 41 mol% guanine plus cytosine. The type strain of Clostridium cellulolyticum sp. nov. is strain Hlo (= ATCC 35319).Anaerobic cellulolytic bacteria that take part in the degradation of cellulosic materials have been isolated from manure, rumen contents, and soil. In this report we describe the isolation and characterization of a new species of Clostridiurn from compost. MATERIALS AND METHODSMedia and culture techniques. The cornposition of the medium which we used was the same as the composition of the cellulose-yeast extract-salts medium (CM medium) described by Weimer and Zeikus (15), except that Na2S was omitted, the cysteine hydrochloride concentration was 1 g/liter, and the cellulose MN300 concentration was 7.5 g/liter.For solid media CM medium was supplemented with 20 g of agar (Difco Laboratories, Detroit, Mich.) per liter. The pH was adjusted to 7.5 with NaOH. This medium was prereduced by the Hungate technique (5) and was dispensed under a constant flow of N2 in 8-ml amounts (4.5-ml amounts for solid medium) into anaerobic culture tubes (16 by 125 mm; Bellco Glass, Inc., Vineland, N.J.).For enrichment cultures, we used anaerobic tubes (25 by 142 mm; Bellco) that contained 25 ml of medium.Carbohydrate media were prepared by replacing cellulose with filter-sterilized solutions of carbohydrates to give final concentrations of 7.5 g/liter. The cultures were incubated at 35°C without shaking.The anaerobic culture techniques of Hungate (5), as modified by Bryant (l), were used throughout this work.All cultures were inoculated and incubated with nitrogen as the gas.Isolation of strain HloT. Strain HloT (T = type strain) was obtained from cultured decayed grass by enrichment and isolation.Enrichment cultures were initiated by inoculating 1 to 2 g of grass from compost into anaerobic culture tubes (25 by 142 mm; Bellco) containing 25 ml of prereduced medium. After 1 week of incubation at 35"C, the cultures were heated at 80°C for 10 min, and 1 ml of each culture was then transferred to 8 ml of prereduced liquid medium.After a few days of incubation, cultures that produced * Corresponding author.discrete gas bubbles and solubilized cellulose were selected for isolation in solid medium. Serial dilutions were incubated in cellulose agar roll tubes. After 3 to 5 days, colonies which produced cleared zones of cellulose digestion were transferred individually into the liquid medium by means of a be...

Various combinations of digestive lipases were tested in vitro under conditions simulating the earlier phases of gastrointestinal lipolysis in the stomach and the duodenum. A solid/liquid test meal was mixed first with either human gastric juice or a solution containing gastric lipase, followed by either the addition of human pancreatic juice and bile or the addition of a solution containing pancreatic lipase, colipase, and bile salts. The rate of lipolysis and the composition of the lipolysis products were assessed as a function of time after lipid extraction and analysis by thin-layer chromatography coupled to flame ionization detection. The lipolytic potential of a crude rabbit gastric extract (RGE) associated with porcine pancreatic extract (PPE) was assessed and compared with the rates of lipolysis of the meal triacylglycerols by human digestive lipases recorded under the same in vitro conditions. RGE combined with PPE appeared to be a good substitute for human gastric and pancreatic lipases. RGE and PPE could therefore be used to simulate the gastrointestinal lipolysis of various foods and emulsions in vitro, as well as that of pharmaceutical lipid formulations.