R. De Schrijver

Glucosinolates in Brassica vegetables: The influence of the food supply chain on intake, bioavailability and human health

Glucosinolates (GLSs) are found in Brassica vegetables. Examples of these sources include cabbage, Brussels sprouts, broccoli, cauliflower and various root vegetables (e.g. radish and turnip). A number of epidemiological studies have identified an inverse association between consumption of these vegetables and the risk of colon and rectal cancer. Animal studies have shown changes in enzyme activities and DNA damage resulting from consumption of Brassica vegetables or isothiocyanates, the breakdown products (BDP) of GLSs in the body. Mechanistic studies have begun to identify the ways in which the compounds may exert their protective action but the relevance of these studies to protective effects in the human alimentary tract is as yet unproven. In vitro studies with a number of specific isothiocyanates have suggested mechanisms that might be the basis of their chemoprotective effects. The concentration and composition of the GLSs in different plants, but also within a plant (e.g. in the seeds, roots or leaves), can vary greatly and also changes during plant development. Furthermore, the effects of various factors in the supply chain of Brassica vegetables including breeding, cultivation, storage and processing on intake and bioavailability of GLSs are extensively discussed in this paper.

Protein digestion in juvenile turbot (Scophthalmus maximus) and effects of dietary administration of Vibrio proteolyticus

The trial was made to study the protein digestion in juvenile turbot during passage of digesta from stomach to rectum. Moreover, diet supplementation with the potential probiotic bacteria, Vibrio proteolyticus, was evaluated with regard to protein digestion. For a 3-week period, fish (25–30 g) were fed by oral intubation and received either a liquid mixture consisting of 40% nonpurified control diet and 60% water or this mixture supplemented with 1010 viable V. proteolyticus ml−1. Daily dry matter intake was 1.5% body weight. As digesta progressed from the stomach to the foregut, hindgut and rectum, the increase in apparent nitrogen digestibility was accompanied by higher ammonia contents, suggesting substantial involvement of the microbiota in protein degradation in the distal segments of the gastrointestinal tract. Water-soluble nitrogen contents were significantly higher in the foregut, presumably corresponding with considerable protein digestion by secreted endogenous enzymes in this digestive segment. Over 65% of the soluble protein in all four parts of the tract had a MW 200,000) increased. Ingestion of V. proteolyticus tended to stimulate apparent nitrogen digestibility (P<0.1). This effect corresponded with increased protein degradation in the proximal intestine as was shown by the significantly elevated fraction of soluble proteins with MW<1000.

Nutrient utilization in rats and pigs fed enzyme resistant starch

The influence of 6% dietary raw or retrograded high-amylose corn starch on protein, fat, carbohydrate, energy and mineral utilization was studied in rats and ileum-cannulated pigs fed the same conventional diets. Ileal nitrogen digestibility tended to decrease and faecal nitrogen excretion to increase in pigs fed one of the tested enzyme resistant starch (RS) sources. In rats, the effect from RS intake on faecal nitrogen excretion was more pronounced (P<0.05). These effects were paralleled by a shift of the nitrogen excretion from the renal to the faecal output. As a result, no significant effects from RS on nitrogen retention could be established in pigs and rats. RS consumption tended to lower apparent faecal fat digestibility in rats as well as apparent ileal and faecal fat digestibility in pigs. This effect on faecal fat digestibility was significant in pigs fed retrograded high-amylose corn starch. Faecal starch digestibility was significantly decreased in rats fed RS. Similar effects were found at the terminal ileum in pigs, but not at the anal level possibly due to more intensive fermentation in the large intestine of these animals. Apparent faecal digestible and metabolizable energy values were significantly lower in rats receiving RS. These effects were less pronounced in pigs, although RS intake significantly lowered apparent ileal energy digestibility when retrograded high-amylose corn starch was fed. In vivo determination of the RS concentrations in both test diets using ileum-cannulated pigs revealed values of 2.9% raw and 5.7% retrograded high-amylose corn starch instead of the 6% RS as measured in vitro, indicating that the tested retrograded starch behaved more like RS in the small intestine as compared with the raw starch. RS did not significantly affect apparent faecal absorption or retention of Ca, P, Mg and Zn in rats and pigs. In pigs, RS intake tended to decrease ileal absorption of the minerals, but these effects appeared to be neutralized in the large intestine. Despite the moderate dietary RS content, increases in faecal water content and bulking were found in rats and pigs. In conclusion, the investigated effects from RS ingestion were in general qualitatively similar in both species. Retrograded high-amylose corn starch, as compared with raw high-amylose corn starch, often exerted more pronounced effects, but the differences were not always significant.

Polychlorinated biphenyls in broiler diets: their digestibility and incorporation in body tissues.

The influence of dietary amounts of polychlorinated biphenyls (PCBs) was studied on performance, apparent PCB digestibility and PCB accumulation in broiler chickens that were maintained until 42 days of age. Dietary concentrations of supplemented PCBs, based on the sum of seven reference congeners, ranged from 0 to 12 ng/g, which was below the legal maximum of 200 ng PCBs/g fat in Belgian feeds. PCB ingestion did not significantly affect body weight and feed intake. Apparent PCB digestibility was not influenced by dietary levels of added fat varying between 4% and 8%, but was significantly higher in broilers fed diets containing added PCBs. Accumulation of PCBs in the fat fraction of abdominal adipose tissue and breast and thigh muscle greatly depended upon PCB intake. However, PCB contents in the various body fat fractions within the same animal differed, even within muscle tissues, indicating an unequal PCB distribution in body fats.

Expansion and pelleting of starter, grower and finisher diets for pigs: effects on nitrogen retention, ileal and total tract digestibility of protein, phosphorus and calcium and in vitro protein quality

The nutritional effects of feed expansion and pelleting were evaluated in digestibility experiments involving 40 castrates (Belgian Landrace×Pietrain) which were kept from 20 to 100 kg of body weight. The animals were successively fed a starter, grower and finisher diet containing barley, wheat, soyabean meal and cassava. The diets were subjected to either expansion at ∼100°C, or pelleting at ∼80°C, or expansion followed by pelleting. The unprocessed control diet was fed as meal. The pigs were divided into four groups and fed one of the experimental diets. With each pig, two 5-day digestibility trials were performed with the starter, grower and finisher diet, respectively. Neither feed intake, weight gain or feed:gain ratio of starting, growing and finishing pigs was significantly (P>0.05) affected by one of the applied feed processing methods. Expansion of the meal diets had no significant effects on protein utilisation as measured by N-retention and apparent ileal and total tract N-digestibility. Feeding of the pelleted grower and finisher diets (without or with preceding expansion) significantly (P<0.05) increased apparent total tract protein digestibility, while ileal protein digestibility, nitrogen retention, and ileal and total tract dry matter digestibility were also improved, but not always significantly at P=0.05. In vitro tests showed that feed processing led to significantly (P<0.05) higher available lysine and had no effect on amounts of free amino acids. Feed expansion tended to decrease protein solubility at alkaline pH, but pelleting caused a significant (P<0.05) increase, which appeared to be paralleled by higher protein digestibility in the growing and finishing pigs. Ileal and total tract digestibility of phosphorus and calcium were impaired when pigs were fed the expanded or pelleted diets. When expansion was followed by pelleting, the negative effects on phosphorus and calcium digestibility were reduced.

Availability of minerals in rats and pigs fed non-purified diets containing inulin

The effect of inulin on Ca, P, Mg, Fe, and Zn utilization was studied in rats and in ileum-fistulated pigs. Apparent ileal and fecal absorption, as well as retention of Ca and P, were lower in animals receiving inulin, whereas fecal absorption of Mg was not changed despite its lower ileal absorption and retention. Absorption of Ca and P in the small intestine was higher than total gastrointestinal absorption, indicating that the colon plays an important role in the utilization of these minerals. Slightly negative retentions of Fe and Zn were observed in animals fed the control diet, as well as in animals fed the diet containing inulin.

Effect of unprocessed and baked inulin on lipid metabolism in normo- and hypercholesterolemic rats

Abstract Male Wistar rats were fed a bread diet containing either corn starch or 6% raw or 6% baked inulin. Furthermore, the diets were either cholesterol-free or contained 1% cholesterol and 0.1% cholic acid. Adding unprocessed or baked inulin to the cholesterol-free diets resulted in significantly lower plasma cholesterol concentrations as well as in decreased liver cholesterol concentrations, while higher daily fecal excretions of bile acids were found. The normocholesterolemic rats showed a tendency to elevated fecal excretion of neutral steroids when inulin was fed, in spite of some decrease in the coprostanol excretion. In these groups there was a significantly inverse linear relationship between liver cholesterol concentrations and daily fecal bile acid output. The results suggest that the cholesterol lowering effect of inulin in normocholesterolemic rats may be due to higher fecal steroid excretion. Moreover, these rats tended to show higher HDLLDL cholesterol ratios when they received one of the inulin containing diets. In the hypercholesterolemic groups no significant effect from inulin intake on the plasma and liver cholesterol concentrations was found. In these rats, fecal cholesterol excretion was significantly increased by 40% when baked or unprocessed inulin was added to the diet, but fecal coprostanol excretion was significantly decreased by 95%. As a consequence, consumption of inulin did not change total neutral steroid excretion in the hypercholesterolemic groups. Moreover, fecal bile acid output was not significantly affected by dietary treatment. The fact that inulin intake did not change total steroid output might explain why plasma cholesterol was not reduced in the hypercholesterolemic rats receiving inulin, in contrast to the results obtained with the normocholesterolemic rats. Also no effect from inulin consumption was found on the HDLLDL cholesterol ratio in the hypercholesterolemic animals. Including inulin in bread did not alter its effect on lipid metabolism, neither in normo- nor in hypercholesterolemic rats.

Consumption of enzyme resistant starch and cholesterol metabolism in normo- and hypercholesterolemic rats

The influence of raw and retrograded high amylose corn starch on cholesterol metabolism in normo- as well as hypercholesterolemic rats was studied. No effect on cholesterol metabolism was observed in normocholesterolemic rats. On the contrary, in hypercholesterolemic animals plasma free and total cholesterol concentrations were significantly lower when enzyme resistant starch was fed. Liver cholesterol concentrations were significantly decreased in rats given the hypercholesterolemic diet supplemented with retrograded high amylose corn starch. Total fecal bile acid excretion and bile acid spectrum were not changed by enzyme resistant starch consumption. Plasma total cholesterol concentrations showed a significantly negative correlation with fecal coprostanol excretion in hypercholesterolemic rats. However, there is no evidence that coprostanol is the only factor responsible for the observed hypocholesterolemic effect of enzyme resistant starch in cholesterol fed rats.

Nitrogen metabolism in rats and pigs fed inulin

This study was conducted to determine the effect of inulin, added to a non-purified diet, on nitrogen metabolism in rats and ileum-fistulated pigs. Ileal and fecal nitrogen excretion in pigs as well as nitrogen retention in both species were not influenced by inulin consumption. Fecal nitrogen excretion was significantly higher in rats fed inulin. This effect was paralleled by a shifting of nitrogen excretion from the renal to the fecal site. Moreover, cecal ammonia concentrations decreased upon feeding inulin, indicating that ammonia was more utilized in bacterial mass production. No effect of inulin intake on plasma urea concentration was found. The observed lowering of intestinal ammonia is an important aspect of inulin consumption as ammonia may interfere with mucosal cell cycle.

Effect of enzyme resistant starch on large bowel fermentation in rats and pigs

Abstract The effect of raw and retrograded high-amylose corn starch, added to a semisynthetic or conventional diet, on the fermentation process in the cecum of the rat and in the proximal colon of the pig was investigated. A trophic effect on the rat cecal wall was observed when both types of diets were fed. Moreover, lower pH values were noted in rats as well as in pigs. There was no general inverse relation between cecal or colonic pH and L-lactic acid concentrations. Rats fed the enzyme resistant starch sources had significantly lower cecal ammonia concentrations, indicating higher bacterial activity resulting in increased conversion of ammonia to bacterial protein. A similar, however non-significant (P=0.06) effect was found in pigs. Generally, the mean cecal concentrations of volatile fatty acids were higher upon resistant starch feeding to rats given semi-synthetic diets, but the effects were only significant for butyrate and total volatile acid concentration when retrograded high-amylose corn starch was supplied. On the contrary, rats receiving resistant starch added to the conventional diet showed no significant influences on cecal butyric acid and total volatile fatty acid concentrations. Also in pigs, no significant effects of enzyme resistant starch intake on colonic volatile fatty acid concentrations were found. No significant effects of enzyme resistant starch intake on portal blood volatile fatty acid concentrations were observed in rats. In general, the amount of butyric acid as part of the total volatile acids was substantially lower in the portal blood as compared with the cecum, suggesting that butyric acid was greatly metabolized by the intestinal wall.