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A study was undertaken to determine whether the reduction of the molar phytic acid/zinc ratio by enrichment of wholemeal and crispbread with zinc improves zinc availability to the same extent as does the reduction of phytic acid in whole meal cereal products. For three weeks, five diets (three samples of wholemeal bread and two samples of crispbread] were fed to growing rats. Significant increases in bone-zinc deposition and activity of serum alkaline phosphatase were induced by those bread samples in which the phytic acid/zinc ratio had been lowered either by enrichment with zinc or by reduction of phytic acid (enzymatic hydrolysis by adjusting the pH-value of the dough with lactic acid) when compared with untreated bread samples. Weight gain of the animals differed little between the groups. The results suggest that it is possible to improve zinc availability in wholemeal cereal products high in phytate by enrichment with zinc.

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The bioavailability of limiting amino acids (lysine, cystine and methionine), which are formed during the germination of wheat and mung beans, was assessed in nitrogen balance trials on growing rats. In addition, the influence of heat treatment on the protein nutritional value of wheat and mung beans was determined. Compared to ungerminated wheat, net protein utilization (NPU) and biological value (BV) increased from 30% and 36% to 41% and 52%, respectively. Apparent protein digestibility (PD) decreased from 82% to 79% during 4 day germination. Heat treatment improved PD from 82% to 85% in ungerminated wheat, but not during germination. NPU and BV were not changed by heat treatment. Feeding germinated mung beans caused a markedly reduced feed intake by the animals, which made it impossible to evaluate changes in protein nutritional value during germination. Heat treatment of ungerminated mung beans improved PD, NPU and BV from 77%, 38% and 49% to 81%, 48% and 60%, respectively. The results indicate that the amino acids, in particular lysine, which are formed in germinating wheat, are available to the rat. Heat treatment will improve considerably the protein nutritional value of ungerminated mung beans.

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Due to its high phytate content, the bioavailability of zinc in whole meal cereal products is distinctly lower as compared to foods of animal origin. The effect of reducing the phytate content of cereal products made from rye and wheat on growth, zinc content of femur and blood serum, as well as on the activity of serum alkaline phosphatase was investigated during a 3-week feeding trial in growing rats. The reduction of phytate was achieved by controlling the phytase activity originally present in cereals. By these treatments, the molar phytic acid/zinc ratio in the cereal products was reduced from 27-37 to 3-18. The four parameters under investigation showed a significant improvement in zinc bioavailability with decreasing phytic acid/zinc ratios. The relevance of these results for man and the value of the molar phytic acid/zinc ratio as an indicator of the bioavailability of zinc in foods are discussed.

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The changes in nutrients during the germination of wheat, mung beans and chickpeas were investigated. Germination was performed under conditions commonly used in the household. The amount of water taken up during 4 days of germination varied from 159 g/100 g (chickpeas) to 450 g/100 g (mung beans). For all three seeds losses of dry matter and carbohydrates were observed. In wheat and mung beans, phytic acid was partially hydrolyzed. In mung beans, the total fat content decreased. Increases in the content of polyunsaturated fatty acids in wheat and of dietary fibre in wheat and mung beans were noted. At a constant level of crude protein, a measurable rise in limiting amino acids was observed in wheat and mung beans. Frequent watering during germination caused losses of Fe, between 9% and 21%, K (27% in chickpeas) and Cu (17% in chickpeas). Except for vitamin B6 in both legumes and vitamin B1 in chickpeas, accumulation of the vitamins under investigation (B1, B2, B6, C, E) was noted. Owing to these changes during germination, the nutritional value of the three seeds has been improved to various extents, most distinctly in wheat and least noticeably in chickpeas. Compared with other vegetables, sprouted seeds can be considered a valuable addition to the diet.

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The effect of various processing methods used for the production of dry flatbread from ground whole rye on the nutritional protein quality were investigated by means of the nitrogen balance method in growing rats. The following products were tested: untreated ground whole rye, baked crisp bread, extruded flatbread without and with the addition of 2.5% and 5.0% of saccharose. The apparent protein digestibility (PD) of the 5 samples varied between 69% and 72% and was neither affected by the method of processing nor by the difference in sugar content. Compared to the untreated raw material (NPU = 41%; BV = 59%) net protein utilization and biological value in crisp bread baked by the traditional method (NPU = 35%; BV = 48%) and in extruded flat bread with 5% sugar (NPU = 35%; BV = 51%) were significantly reduced (P less than 0.05). In extruded flatbread without and with 2.5% sugar, NPU and BV of the raw material were essentially maintained. The results indicate that in comparison with the baking process the extrusion of flatbread is more suitable to protect the protein quality. The addition of more than 2.5% sugar caused protein damage in extruded flatbread, presumably as a result of Maillard reactions.

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Metabolic faecal nitrogen excretion was assessed in 8 young rats (90-100 g body weight) following an oral application of 75 mg 15N-glycine (95 atom-% 15N). Four rats received an experimental diet containing 12% cellulose, while a control diet containing 4% cellulose was fed to the remaining 4 animals. The high cellulose content induced a highly significant reduction of the N balance due to a greatly increased urinary N excretion. The metabolic faecal nitrogen was determined by measuring 15N excretion in faeces and urine from day 5 (3) to day 8 following 15N glycine administration. During this time interval 15N elimination follows an exponential curve. Increasing the dietary cellulose content from 4 to 12% produced a rise in metabolic faecal nitrogen from 13.9 to 15.7 mg/day and in total faecal nitrogen from 21.3 to 24.4 mg/day. From these values a mean true protein digestibility of 98% was calculated for both groups of rats, regardless of the difference in dietary cellulose content. The fraction of endogenous faecal nitrogen which is of bacterial origin was determined through the analysis of 2, 6-diamino-pimelic acid (DAP). The added cellulose in the experimental diet caused a rise in faecal DAP from 0.302 to 0.402 mg/day corresponding to an increase of bacterial nitrogen from 5.2 to 6.4 mg/day. Accordingly the observed rise in endogenous faecal nitrogen is largely due to increased bacterial nitrogen.

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Using a Creusot-Loire twin-screw extruder (Type BC 45), ground soy bean and whole rye meal were extruded under various processing conditions (12% and 18% water content in the raw material, 129 degrees C and 165 degrees C product temperature in the case of soy bean, 12% and 18% water content, 165 degrees C product temperature in the case of rye, screw speed of 150 R/min, for all samples). The nutritional protein quality (apparent protein digestibility PV, net protein utilization NPU, and biological value BW) of the extrudates was determined by the nitrogen balance technique in growing rats. Compared to the untreated raw material no decrease in PV or NPU was noted for extrudates made from soy bean or rye. Extrusion of ground soy bean at 165 degrees C and 18% water content caused a significant decrease of BW from 68% to 64%. The lower water content (12%) induced a slight improvement of PV in soy extrudates and of NPU and BW in rye extrudates. The results indicate that the extrusion at low water content and moderate temperature can safely be used to process ground soy bean and whole rye meal without and damage to the nutritional protein quality.

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A simple method is described by which the fecal flora of rats has been isolated with high recovery and a high purity grade. Total nitrogen and 2.6-diamino-pimelic acid were determined in the isolated bacteria. From both values a factor was calculated, which permits the estimation of fecal bacterial nitrogen from fecal DAP content. In the feces of rats on a semisynthetic control diet (4% cellulose) this factor was 15.7. Addition of 8% guar (by substitution for starch) resulted in a drastic increase in fecal DAP content thus lowering the factor to 11.5. When the proportion of cellulose in the control diet was raised from 4 to 12%, no change in the factor was observed. This indicates a pronounced effect on the bacterial activity by guar but not by cellulose. It is concluded that the factor used to calculate fecal microbial nitrogen from fecal DAP content is dependent on the kind of dietary fiber ingested.

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The metabolic fecal nitrogen was determined in 8 young rats (90-100 g body weight) using a single oral dose of 75 mg 15N-glycine. Four rats were fed a diet containing 8% guar and 4 rats received a control diet without guar. Compared to the control group, apparent protein digestibility and nitrogen balance were significantly lower in the guar group. After an initial steep rise the 15N-elimination in feces and urine (days 2-8 after 15N-glycine application) followed an exponential curve in at least 2 phases, with increasing half-time values. The proportion of metabolic fecal nitrogen to total fecal nitrogen was calculated from the 15N-atom-% excess, determined daily in urine and in feces. This calculation is based on the assumption that the specific 15N-activity (15N-atom-% excess) in urine represents the specific 15N-activity of the endogenous nitrogen pool. The addition of guar raised the proportion of metabolic fecal nitrogen from 51% (control) to 73%, corresponding to an increase in total fecal nitrogen loss (24 mg) observed in the guar-fed animals. This indicates that the rise in fecal nitrogen loss caused by guar is due almost entirely to enhanced secretion of endogenous nitrogen and not to undigested food protein. Based on the analysis of 2,6-diamino-pimelic acid in the feces of 4 rats the proportion of bacterial nitrogen in the feces was calculated. It amounted to 19.8% of total fecal N in the control group, and to 30.1% in the guar group, or to 39.4% and 44.4% of metabolic fecal nitrogen respectively. Obviously the increased dietary fiber intake also caused a rise in the amount of metabolic fecal nitrogen, which is derived from gastro-intestinal secretions and epithelial tissue.

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The effect of carob bean gum (9.5 g/1000 kcal, 4184 kJ) in the daily diet on the absorption of Ca, Fe, Zn and Cu was determined during a 4-week balance study in 2 male and 6 female healthy subjects, aged 19 to 25 years. A normal mixed diet was used, to which carob bean gum was added during food preparation for the last 2 weeks of the study. The absorption of minerals and trace elements was calculated as the difference between dietary intake and fecal excretion. The ingestion of carob bean gum caused a significant reduction in the absorption of Ca, Fe and Zn when compared to the control diet, while the absorption of Cu remained unchanged.

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The effect of "indigestible" polysaccharides fed at the 10% level in a semi-synthetic diet on absorption of Ca, Fe, Zn, Cu, Cr and Co, on weight gain and on fecal dry matter excretion was studied over a period of 8 days in five groups of 12 weanling male rats each and compared to a control group. Carrageenan (C) and agar-agar (AA) reduced absorption of all minerals tested, Na-alginate (NA-A) decreased Fe-, Cr- and Co-absorption, carob bean gum (CBG) and gum guar (GG) interfered with the absorption of Zn, Cr, Cu and Co. In a second study the long-term effect of GG and AA-ingestion at the 10% dietary level on mineral absorption was investigated during three 4-day balance periods of a 21-week feeding trial in 24 young rats. Mineral content of rat carcasses, assayed at the termination of the experimental period, did not reveal any significant differences between controls and animals fed AA or GG, suggesting that the rat is able to compensate for the increased fecal losses, presumably by reduced urinary losses. Ingestion of AA, C or Na-A resulted in a marked increase of fecal dry matter, indicating that hardly any of these substances were degraded, whereas a considerable portion of GG and CBG was metabolized, presumably due to the action of intestinal bacteria.

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The effect of oxygen elimination during irradiation (5 Mrad) and subsequent storage, storage time (12 weeks), degree of lipid-unsaturation and added antioxidant (vitamin E) in protein-lipid mixtures (casein : fat - 11.1 : 4) on the nutritive value of protein was studied during 8-day nitrogen balance trials in 12 groups of 6 weanling rats each. When casein-cocofat-cornoil mixtures were irradiated and stored under aerobic conditions a reduction of NPU appeared upon prolonged storage time, which was prevented by excluding oxygen during irradiation and storage. When the lipid component consisted entirely of cocofat no loss in NPU occurred under aerobic processing and storage conditions throughout the 12 week storage period. Replacement of cocofat through sunfloweroil resulted in a drastic reduction of NPU and in growth inhibition, which was not prevented by the addition of vitamin E (0.05 g/100 g lipid). Irradiation of casein-lipid mixtures resulted in a significant increase of carbonyl compounds. A further increase was effectively prevented by elimination of oxygen during irradiation and storage. A drastic increase of carbonyl compounds as well as a significant reduction of available lysine occurred in casein-sunfloweroil mixtures. Added vitamin E afforded only limited protection against these changes.

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The effect of five indigestible polysaccharides (IP) of different origin and chemical structure on N balance and dry matter digestibility was studied in growing rats. The diets contained 10% of gum guar (GG), carob bean gum (CBG), Na-alginate (Na-A), agar-agar (AA) or carrageenan (C), respectively. Dry matter digestibility and apparent protein digestibility were significantly decreased below control values by all 5 IP. N retention was significantly lower after ingestion of AA or C. In the rats receiving GG, CBG or Na-A urinary N excretion was reduced, thus compensating for increased fecal N losses by these animals. The different effects of the 5 substances on N balance are attributed to their partial breakdown through the action of intestinal microflora and/or their ability to partially inhibit the activity of proteolytic enzymes in the gastrointestinal tract. Trypsin inhibition in vitro was observed for C only. Suitability of the various IP as bulking agents in reducing diets is discussed.

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The addition of 5% gum guar to a diet containing 10% casein did not change the overall N retention of young rats but induced a significant shift in the N excretion from urine to feces, resulting in a markedly decreased apparent protein digestibility. The increase in total fecal dry matter over control values accounted for only 30% of the ingested gum guar implying that 70% was absorbed, possibly after being degraded by intestinal micro-organisms. The elimination of 14C activity following oral application of 14C protein indicated an accelerated turnover of amino acids during the first 3 h. After 25 h no difference between experimental and control animals was evident with respect to 14C activity remaining in the carcass. The transit time of food, as determined by neutron activation analysis of an Ytterbium marker, was somewhat decreased in the presence of gum guar.

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Approximately 8--10 days after gum guar was added to the diet of rats, the total bacterial counts in their feces, in particular Clostridium and Lactobacillus, were increased, whereas the number of coliforms was reduced. In contrast to the long, slender, rod-shaped cells in the Gram-stained fecal smears of the control animals, the feces of the gum guar-fed animals showed a predominance of short, broad, Gram-positive rods. When gum guar was omitted from the diet of these animals, their feces could not be distinguished from those of control animals.

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The effect of radiation sterilization on casein alone and in the presence of glucose or starch was assessed by means of nitrogen balance studies in growing rats and compared to the effect of heat sterilization. No decrease in protein digestibility and utilization was noticed in the irradiated samples nor did the presence of glucose or starch during processing cause and changes of these parameters. Following heat sterilization of casein in the presence of glucose there was a significant reduction in protein digestibility and Net Protein Utilization (NPU). These changes were accompanied by a drastic decline of available lysine. The inclusion of 3% agar-agar (aqueous solution) in the diet induced a drastic rise in endogenous faecal nitrogen losses and a corresponding decrease in apparent protein digestibility and NPU.

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