Angela Sotelo

Effect of different alkalies, temperature, and hydrolysis times on tryptophan determination of pure proteins and of foods.

A comparative study was carried out in order to determine which of the most commonly used alkalies for protein hydrolysis in tryptophan determination gave the best results. Hydrolyses were performed with 2.5 and 4 n Ba (OH)2, 4 and 10 n NaOH, 5 n NaOH containing 5% SnCl2, and with 4 n LiOH, not previously reported for use. The effect of temperature and hydrolysis time on the measured tryptophan content was also determined. Based on results obtained with lysozyme and with seven high protein preparations 4 n LiOH gave the best results. A temperature of 145°C was selected as the most convenient temperature since maximum tryptophan values were obtained with 4–8 h. The hydrolysis time required was inversely related to the protein content of the preparation. Lysozyme, casein, bovine plasma protein, and dehydrated whole egg gave maximum tryptophan content after 4 h hydrolysis while skimmed milk powder, rice flour, wheat flour, and wild legume flour required 8 h hydrolysis.

Comparative study of the chemical composition of wild and cultivated beans (Phaseolus vulgaris)

Five wildPhaseolus vulgaris beans were compared with five cultivatedPhaseolus vulgaris beans in proximate composition, total (true) protein, amino acid composition, and toxic and antinutritional factors. The wild beans contained more protein (25.5% vs. 21.7%), ash (5.15 vs. 4.15%), crude fiber (7.08% vs. 5.04%) compared to cultivated beans while the former contained less fat (0.56 vs. 0.89%) and carbohydrates (61.64 vs. 68.05%). Sulfur amino acids were found to be limiting in both groups of bean as expected; however, the cultivated beans had a higher content of the limiting amino acids. Therefore, the cultivated beans showed a better amino acid profile than the wild beans. Toxic factors were not found in either type of bean; the determinations included saponins, alkaloids, and cyanogenic glycosides. The antinutritional factors investigated were hemagglutinins (lectins) and trypsin inhibitors. The wild beans presented a higher content of trypsin inhibitors (28 TUI per mg) and lectins (9.6) than the cultivated beans did (21 TUI per mg and 7 respectively). From the chemical point of view, domestication seems to be positive; however, the better protein nutritive quality of the cultivated beans should be further confirmed by biological assays.

Nutritional value and content of antinutritional compounds and toxics in ten wild legumes of Yucatan Peninsula.

The chemical and toxicological composition of ten wild legumes collected in Yucatan, Mexico was determined. For each species the whole fruit, (seed and pod), were studied as well as the seed and pod separately. A higher protein content was found in the seeds ofA. lebbeck andP. saman (37.07 and 37.60% respectively). In the seeds ofL. longystilus, C. yucatanensis andP. keyense a high concentration of fat was found, especially in the first with 31.34%. A high quantity of fiber was found in the pods. In general, the samples were rich in lysine (especially seeds) and scant in sulfur amino acids and tryptophan. All the samples showed high concentration of potassium and calcium. Some of them exhibited significant concentrations of iron. The pods ofP. saman and P. keyense showed a high content of lectins. In the seeds ofC. yucatanensis and in the pod ofP. keyense high concentrations of trypsin inhibitors were found 60 and 406.7 TUI/mg sample respectively. The presence of saponins, was detected in seven samples, of which the seed ofP. keyense had the highest concentration. Alkaloids were found only in the whole fruit and pod ofP. saman and cyanogenic glucosides were present inA. pennatula. In general terms, the whole legume showed better digestibility than the pods alone.

Role of oxate, phytate, tannins and cooking on iron bioavailability from foods commonly consumed in Mexico

Abstract The objectives of this research were to assess the bioavailability of iron in foodstuffs found in the Mexican diet, to provide data on the content of iron absorption inhibitors present in plant origin products and to assess the inhibitory effect of these compounds and of cooking on iron bioavailability; therefore, total content and bioavailable iron, tannins, phytic and oxalic acid were determined in vegetables, cereals, legumes and animal products, before and after cooking. Vegetables, although rich in iron, have poor iron bioavailability and a high content of inhibitory factors; cooking reduced the content of iron and inhibitory factors, whereas in animal products the treatment of cooking did not significantly reduce it. Iron bioavailability, phytate content and the phytate to iron molar ratio predicted poor iron bioavailability and, therefore, a negative impact on the nutritional status of people who rely on them as staple foods could be expected.

Silage preparation from tuna fish wastes and its nutritional evaluation in broilers

The present study was conducted to obtain tuna waste silage from the canning industry by using fresh fish viscera for the autolytic process. Chemical characterisation of the product and nutritional evaluation for broiler diets were then carried out. Three types of studies were performed. In study one the proximal composition was measured and three acid mixtures were tested for silage development. The formic–sulphuric acid mixture was chosen. The measurement of non-protein nitrogen (NPN) formation indicated that more than 50% NPN was obtained after 2 days of storage; pH changes were also measured and stabilisation occurred after 24 h. Contents of aerobic mesophiles, total coliforms, yeast and mould were reduced during the first month of storage. Study two was then conducted to determine the proteolytic activity in fresh viscera, the changes in lipid oxidation and the trimethylamine formation during silage development. It was observed that cooked dark meat wastes were oxidised at the beginning, but trimethylamine did not change during 2 months of storage. Thirty-nine per cent of tryptophan content was lost, but available lysine decreased only 8% from original content after 20 days of storage. Fe, Ca, P, Zn, Na and K contents were also measured. A larger batch of silage was obtained and dried after sorghum addition. The silage–sorghum ratio was 70:30. Four starter diets for 9-day-old broiler chicks were prepared at different levels from the final dried silage (5, 10 and 15%). The control diet (0%) contained soybean meal as the predominant protein supplement. Food intake, weight gain and feed conversion were recorded during the short-time feeding study. There were no significant effects of dietary inclusion on the final dried product (p < 0.05). The results showed that 15% of this product can be included without adverse effects on broilers. © 1999 Society of Chemical Industry

Amino acid determination in pure proteins, foods, and feeds using two different acid hydrolysis methods

Abstract To compare the rapid acid hydrolysis (proposed by Gehrke) to the classic acid hydrolysis method, the amino acid content in 15 samples of animal and vegetable nature, with variable quantities of protein and other nonproteic components, were determined following the two methods of acid hydrolysis using 6 n HCl at 110°C for 24 h and at 145°C for 4 h. Because the high-temperature, short-time hydrolysis (HTST) method has been used only in pure proteins, the purpose of the present work was to confirm that it could be applied to any material, especially foods and feeds. Three groups of samples were tested: pure proteins, protein concentrates, and vegetable samples with a high carbohydrate content. The acid hydrolysis by the two methods was performed in duplicate. The statistical analyses (Students t test) of the total amino acids and the total essential amino acids indicated no differences between the two methods in any of the three groups of samples. In the group of protein concentrates there appeared differences in only three amino acids: in valine (higher values by the HTST method) and in aspartic acid and serine (lower values by the HTST method). These results indicate that the HTST hydrolysis method is equivalent to the classic method and can be used for any type of material. The use of this method can also save considerable time in the determination of amino acids, especially in food analysis.

The nutritional quality and toxin content of wild and cultivated lima beans (Phaseolus lunatus)

Proximal analysis, amino acid profile, trypsin inhibitor content, hemagglutinin content and HCN generated from cyanogenic glucosides were determined in four wild and three cultivated varieties ofPhaseolus lunatus. All the wild beans showed a higher protein content than the cultivated beans, but no big differences were found in the other nutrients. The essential amino acid percentage was higher in the cultivated beans than in the wild seeds, which was reflected in the PER determination. The most remarkable difference found between wild and cultivated beans was the high concentration of HCN in all wild varieties. The high concentration of protein found in the wild seed could be a false result from the nitrogen provided by the cyanogenic glucosides.

Chemical Composition and Toxic Factors Content in Fifteen Leguminous Seeds

AbstractThe proximate analysis performed on 15 leguminous seeds showed that the protein content ranged from 10 to 31.54% and fat was 10% in most of the samples (only two had 24.4 and 27.6%, respectively). Crude fiber was greater than 16% in nine seeds and only six had less than 16%. Sulfur containing essential amino acids were limiting in all the seeds and in one of them, tryptophan was the first limiting amino acid. All the samples had trypsin inhibitors and in one of them the content was very high (240 TUI). Only two samples showed hemagglutinating activity and only one produced hemolysis. None of the seeds gave a positive response for alkaloids.

Chemical and Nutritional Composition of Tejate, a Traditional Maize and Cacao Beverage from the Central Valleys of Oaxaca, Mexico

Foam-topped cacao and maize beverages have a long history in Mesoamerica. Tejate is such a beverage found primarily in the Zapotec region of the Central Valleys of Oaxaca, Mexico. Historically tejate has been ceremonially important but also as an essential staple, especially during periods of hard fieldwork. However, the nutritional contribution of traditional foods such as tejate has not been investigated. We analyzed tejate samples from three Central Valley communities, vendors in urban Oaxaca markets and one migrant vendor in California, USA for their proximate composition, amino acid content and scores, and mineral and methylxanthine content. Nutritional and chemical variation exists among tejate recipes, however, the beverage is a source of energy, fat, methylxanthines, K, Fe and other minerals although their availability due to presence of phytates remains to be determined. Tejate is a source of protein comparable to an equal serving size of tortillas, with protein quality similarly limited in both. Tejate provides the nutritional benefits of maize, and some additional ones, in a form appealing during hot periods of intense work, and year round because of its cultural significance. Its substitution by sodas and other high glycemic beverages may have negative nutritional, health and cultural consequences.

Nutritive value of diets containing fish silage for juvenile Litopenaeus vannamei (Bonne, 1931)

BACKGROUND Fish wastes has been used for many years as an alternative in feeds for aquaculture. In the present study weight gain of juvenile white shrimp Litopenaeus vannamei fed diets including fish waste silage (WS), fish waste silage with soybean meal SBM (WS + S) or fish waste meal (WM) was compared. A conventional acidic silage process was applied to obtain from wastes (skin, heads, bones and viscera) of snapper (Lutjanus spp.), grunt (Haemulon plumieri), and grouper (Epinephelus spp.) an ingredient rich in protein. RESULTS After 3 days ensilage more than 90% protein was hydrolysed. Waste material processed at pH 3.8 lost about 24% tryptophan. Butylated hydroxytoluene (BHT) prevented lipid oxidation, as shown after 45 days with malonaldehyde production. Shrimp fed WS + S diet gained 0.7 g per week higher than those fed WS and WM diets with 0.3 g per week (P < 0.05). CONCLUSION WS processed with formic acid under conditions of low pH is beneficial for the white shrimp L. vannamei. It sustained reasonable weight gain combined with soybean meal in practical diets. On the other hand, BHT addition was beneficial in preventing oxidative action during silage preparation.