Storage of milk powders under adverse conditions: 2. Influence on the content of water-soluble vitamins

1. Storage of milk powder under unfavourable conditions accelerates the normally slow deterioration in nutritional quality. The effects of such storage on the water-soluble vitamin composition were examined. 2. (a) Spray-dried whole milk containing 25 g water/kg was stored at 60° and 70° and sampled weekly to 9 weeks. (b) Spray-dried whole milk and skimmed milk were adjusted to contain 40 and 100 g water/kg and stored at 37° in nitrogenand in oxygen. Samples were taken for analysis at intervals during storage. 3. The samples were analysed for eight B-complex vitamins and ascorbic acid, and also for total lysine, ‘reactive lysine' and ‘lysine as lactulosyl-lysine'. 4. Storage at 60° caused rapid destruction of folic acid (53% loss at 4 weeks) and slower loss of thiamin, vitamin B6 and pantothenic acid (18% at 8 weeks). There was no change in the content of riboflavin, biotin, nicotinic acid and vitamin B12. At 70° the rate of destruction of the four labile vitamins was much increased; 18% or less survived at 4 weeks. 5. At 37° and 40 g water/kg there was little change in total and ‘reactive' lysine during storage for 57 d. Lactulosyl-lysine was demonstrably present butatlow concentration. There was considerable loss of folate (72%) and ascorbate (91%) during storage for 30 d in O2, but no significant loss in N2. Thiamin fell by approximately 12% in 57 d, equally in O2 and N2. The content of the remaining vitamins was unchanged. At 100 g water/kg there were progressive Maillard changes. During 27 d in N2 the colour changed from cream to palebrown, but in O2 there was no perceptible colour change. Total lysine fell by 20% in 27 d, and ‘reactive lysine' by 30%. Folate was stable during 16 d in N2, but largely (94%) destroyed in O2. Ascorbic acid was also destroyed in N2 as in O2. Thiamin fell by 41% in 27 d, equally in O2 and N2. Vitamin B6 was more labile, especially in N2, falling by 71% in 16d. 6. With skimmed-milk powder containing 100 g water/kg, storage at 37° in O2 and N2 gave much the same results as for the corresponding whole-milk powder. The presence of milk fat had no marked effect on the stability of the water-soluble vitamins. 7. Destruction of vitamins was clearly linked to the progress of Maillard-type reactions and was strongly influenced by time and temperature of storage, moisture content and, in some instances, by the presence of O

Reactions of proteins with oxidizing lipids: 2. Influence on protein quality and on the bioavailability of lysine, methionine, cyst(e)ine and tryptophan as measured in rat assays

1. The consequences of reactions between protein and oxidizing lipids on the nutritional quality of food proteins have been investigated using a whey protein-methyl linolenate-water model system. 2. In rat assays, significant reductions were observed in protein efficiency ratio, net protein ratio, net protein utilization, biological value and true nitrogen digestibility, especially when the reaction had taken place at high moisture content, high temperature and in the presence of excess oxygen. 3. The losses of bioavailable lysine and tryptophan as measured by rat assays followed a similar pattern. The chemical value of each amino acid multiplied by the true N digestibility closely resembled the rat assay value. In general, the reaction products of lysine and tryptophan formed during lipid oxidation were biologically unavailable. 4. The bioavailabilities of methionine and of ‘methionine plus cyst(e)ine' were determined in separate assays. Cyst(e)ine was calculated as ‘methionine plus cyst(e)ine' minus methionine. In whey protein which had reacted with oxidizing methyl linolenate, the bioavailable methionine content was not significantly reduced even though 82% of the methionine residues were present as methionine sulphoxide. In hydrogen peroxide-treated casein in which all methionine residues were oxidized to the sulphoxide, methionine sulphoxide was found to be 96% as utilizable as a methionine source to the rat. Free methionine sulphoxide was 87% utilizable. 5. Cyst(e)ine appeared to be as sensitive as lysine to reactions with lipid oxidation products. In whey protein which had reacted with oxidizing methyl linolenate, the bioavailabilities of cyst(e)ine, lysine, tryptophan and methionine were reduced by 28, 24, 11 and 8% respectively and true N digestibility by 9%. These results are discussed in relation to food product

Storage of milk powders under adverse conditions: 1. Losses of lysine and of other essential amino acids as determined by chemical and microbiological methods

1. Whole-milk powders containing 25 g water/kg were stored for up to 9 weeks in sealed aluminium containers at elevated temperatures. Lysine and other essential amino acids were measured by chemical and microbiological methods. 2. Storage at 60° resulted in the progressive formation of lactulosyl-lysine. After 9 weeks, 30% of the lysine groups were present in this form. The powders still retained their natural colour and the levels of tryptophan, methionine, cyst(e)ine and leucine remained unchanged. 3. Storage at 70° resulted in the formation of lactulosyl-lysine followed by its complete degradation with the development of browning. Available tryptophan, methione, leucine and isoleucine decreased progressively during storage. 4. The different methods for lysine determination gave widely dissimilar results. The direct fluorodinitrobenzene (FDNB) technique and reactive lysine from furosine were considered to be the most reliable methods. The FDNB-difference, dye-binding lysine, Tetrahymena and Pediococcus methods all seriously underestimated reactive or available lysine in heat-damaged milk powders. Tetrahymena and Pediococcus appeared to utilize lactulosyl-lysine as a source of lysine. 5. The results are discussed in relation to storage and distribution of milk powders in hot climate

Protein-polyphenol reactions: 1. Nutritional and metabolic consequences of the reaction between oxidized caffeic acid and the lysine residues of casein

1. Studies were made on the lysine content of casein reacted with caffeic acid oxidized aerobically under alkaline conditions or enzymically with tyrosinase (EC 1.14.18.1). 2. Loss of fluorodinitrobenzene (FDNB)-reactive lysine was rapid at pH 10 and increased with time and the temperature of the reaction, with concentration of caffeic acid and with the oxygenation of the mixture. In presence of the enzyme mushroom tyrosinase, maximum reduction of reactive lysine occurred at pH 7 and was dependent on the reaction time and on the concentration of caffeic acid. 3. Reaction of α-formyl-L-[U- 14C]lysine with caffeic acid at pH 10 showed the rapid formation of five reaction products which appeared to polymerize gradually as the reaction progressed. 4. The nutritionally available lysine content of the casein-caffeic acid mixtures, as assayed with rats, was reduced after both alkaline and enzymic reactions, as were faecal digestibility, net protein ratio and net protein utilization. Biological value however was not reduced. 5. In metabolic studies using goat milk casein labelled with L-[3H]lysine and reacted with caffeic acid in the same way, the lysine-caffeoquinone reaction products were not absorbed by the rat but were excreted directly in the faeces. 6. The importance of the reaction of proteins with caffeoquinone and chlorogenoquinone (formed by the oxidation of caffeic and chlorogenic acids respectively) is discussed in relation to the production of sunflower protein, leaf protein and other vegetable-protein concentrate

The effect of Maillard reaction products on zinc metabolism in the rat

The effect of giving Maillard reaction products (MRP) on zinc metabolism was investigated in the rat. In Expt 1, MRP were prepared by incubating casein with either glucose or lactose under controlled reaction conditions, and were quantified as either ‘early' or ‘advanced' after estimation of lysine loss and lysine destruction respectively. In Expt 2, the effect of the purified early MRP fructose-lysine (FL) on Zn metabolism was studied. The experimental diets containing 20 mg Zn/kg were given to weanling rats for 21 d. Zn balance was assessed over 9-14 d (Expt 1), or 1-14 d (Expt 2). Femur, liver, kidney and serum Zn concentrations were determined at 21 d. The major effect of the MRP in the casein-sugar mixtures was on urinary Zn excretion. The casein-glucose MRP induced up to a 6-fold increase in the quantity of Zn excreted in the urine. The magnitude of the hyperzincuria increased with the extent of the Maillard reaction. Similar dietary levels of casein-lactose MRP increased urinary Zn loss 2-fold. Free FL had no effect on urinary Zn. Faecal Zn, Zn retention, liver, femur and serum Zn were generally not influenced by giving MRP from casein-sugar mixtures or by giving free FL, although kidney Zn was decreased in rats fed on FL. It was concluded that although urinary Zn excretion can be increased by the presence of MRP in the diet, this is only a minor excretory pathway and would have little influence on overall Zn nutrition in individuals fed on a diet adequate in Z

Stability of tryptophan during food processing and storage: 1. Comparative losses of tryptophan, lysine and methionine in different model systems

1. The stability of tryptophan was evaluated in several different food model systems using a chemical method (high pressure liquid chromatography after alkaline-hydrolysis) and rat assays. Losses of tryptophan were compared with the losses of lysine and methionine. 2. Whey proteins stored in the presence of oxidizing lipids showed large losses of lysine and extensive methionine oxidation but only minor losses of tryptophan as measured chemically. The observed decrease in bioavailable tryptophan was explained by a lower protein digestibility. 3. Casein treated with hydrogen peroxide to oxidize all methionine to methionine sulphoxide showed a 9% loss in bioavailable tryptophan. 4. When casein was reacted with caffeic acid at pH 7 in the presence of monophenol monooxygenase (tyrosinase; EC 1.14.18.l), no chemical loss of tryptophan occurred, although fluorodinitrobenzene-reactive lysine fell by 23%. Tryptophan bioavailability fell IS%, partly due to an 8% reduction in protein digestibility. 5. Alkali-treated casein (0.15 M-sodium hydroxide, 80°,4 h) did not support rat growth. Chemically-determined tryptophan, available tryptophan and true nitrogen digestibility fell 10, 46 and 23% respectively. Racemization of tryptophan was found to be 10% (D/(D+L)). 6. In whole-milk powder, which had undergone ‘early' or ‘advanced' Maillard reactions, tryptophan, determined chemically or in rat assays, was virtually unchanged. Extensive lysine losses occurred. 7. It was concluded that losses of tryptophan during food processing and storage are small and of only minor nutritional importance, especially when compared with much larger losses of lysine and the more extensive oxidation of methionin

Iron bioavailability in two commercial cultivars of wheat: a comparison between wholegrain and white flour and the effects of nicotianamine and 2'-deoxymugineic acid on iron uptake into Caco-2 cells

Iron bioavailability in unleavened white and wholegrain bread made from two commercial wheat varieties was assessed by measuring ferritin production in Caco-2 cells. The breads were subjected to simulated gastrointestinal digestion and the digests applied to the Caco-2 cells. Although Riband grain contained a lower iron concentration than Rialto, iron bioavailability was higher. No iron was taken up by the cells from white bread made from Rialto flour or from wholegrain bread from either variety, but Riband white bread produced a small ferritin response. The results probably relate to differences in phytate content of the breads, although iron in soluble monoferric phytate was demonstrated to be bioavailable in the cell model. Nicotianamine, an iron chelator in plants involved in iron transport, was a more potent enhancer of iron uptake into Caco-2 cells than ascorbic acid or 2'-deoxymugineic acid, another metal chelator present in plants

Giving Miss Marple a makeover : graduate recruitment, systems failure and the Scottish voluntary sector

The voluntary sector in Scotland, as across the globe, is becoming increasingly business like. Resultantly, there is an increasing demand for graduates to work in business and support functions. In Scotland, however, despite an oversupply of graduates in the labor market, the voluntary sector reports skills shortages for graduate-level positions; a leadership deficit was also reported in countries such as the United States. Through exploratory, mainly qualitative, case study and stakeholder research, this article proposes that one reason for this mismatch between the supply of and demand for graduates is a systems failure within the sector. Many graduates and university students remain unaware of potentially suitable paid job opportunities, in part because of the sector's voluntary label. To rectify this systems failure, thought needs to be given to the sector's nomenclature and the manner in which voluntary sector organizations attract graduate recruits, for example, through levering value congruence in potential recruits