NUTRITIONAL STUDIES ON YEASTS DURING BATCH AND CONTINUOUS FERMENTATION. I. CHANGES IN VITAMIN CONCENTRATIONS

The changes in the concentrations of eight vitamins were followed during the fermentation of wort by Saccharomyces carlsbergensis in plant scale batch fermentor, pilot tower fermentor and laboratory-size continuous stirred tank reactor. During fermentation in batch fermentor, p-amino benzoic acid concentration increased fivefold, while pantothenate increased threefold with one yeast but showed a slight drop with another. Riboflavin and inositol concentrations changed only slightly; biotin and pyridoxin concentrations decreased two to threefold, but the nicotinic acid and thiamine concentrations dropped ten to twentyfold. The other fermentation systems gave, in general, different values, but trends similar to the changes observed during batch fermentations were evident. The concentrations of nicotinic acid, thiamine and p-amino benzoic acid (one yeast) in the beer at the end of storage had increased one and one-half to twofold over the concentrations at the end of fermentation; the other vitamins showed little change.     

RHEOLOGY OF PURE AND MIXED KAPPA-CARRAGEENAN GELS IN LACTIC ACID FERMENTATION CONDITIONS

Texture profile analysis and rupture tests, respectively, at a deformation of 5 and 80%, were carried out on commercial kappa-carrageenan gel cylinders (3% w/v concentration) and on mixed gel cylinders (kappa-carrageenan/iotacarrageenan or locust bean gum [LBG], in different proportions), to select the best gel composition as an immobilization matrix for continuous lactic acid fermentations of dairy media. Mixed gel cylinders were soaked in a model system for lactic fermentations consisting of 36 dairy media: milk, whey and whey permeate, with 4 lactate concentrations (5, 20, 35 and 50 g/L of medium), combined with 3 pH values (6.5, 6.0, 5.5). GENUGEL X-0909 n°5180850 was the most resistant of all commercial kappa-carrageenans available; mixing this kappacarrageenan with LBG in the respective proportions of 2.75%/0.25% gave the best rheological properties to the resulting mixed gel. Our study of the impact of fermentation parameters showed that pH has a significant effect on hardness, cohesion and percentage of deformation at rupture in milk (but not in the other 2 media). A pH drop of milk from 6.5 to 5.5 resulted in more brittle gels which may be explained by an increase in the amount of soluble calcium cations. Generally, soaking in milk produced the most brittle gels due to its calcium content, whey produced the hardest gels and whey permeate, the softest. An increase in the amomonium lactate concentmtion significantly improved hardness, rupture force and percentage of deformation at rupture, while reducing cohesion and resilience: NH₄+ cations would account for this effect. The differences in rheological behuviour of immobilization gel beads during continuous Eactic fermentations of milk and whey permeate would be due to the cation content and more specijically to the higher calcium concentmtion in milk.     

LACTIC ACID BACTERIA AND MALOLACTIC FERMENTATION IN THE MANUFACTURE OF SPANISH CIDER

Numeration, isolation and identification of the lactic acid bacteria found in Asturian cider during processing and storage has been carried out. The species Leuconostoc oenos was predominant during both alcoholic and malolactic fermentations. In most of the ciders studied the malolactic fermentation and the alcoholic fermentation started at the same time; production of D-lactate as well as a decrease of L-lactate were to be found once the malolactic fermentation was complete .     

CHANGES IN QUALITY ATTRIBUTES DURING STORAGE OF TOGWA, A LACTIC ACID FERMENTED GRUEL

Microbiological, physicochemical and sensory quality changes in togwa during storage at ambient tropical temperatures were monitored in unpasteurized and pasteurized samples with added sodium benzoate, potassium sorbate, propionic acid or a combination of sodium benzoate and potassium sorbate. The untreated samples were unacceptable within 48 h after production. Organic acids, volatile flavor compounds and fermentable sugars were monitored in untreated samples for up to 96 h. Ethanol, 2-methyl-1-propanol, 2-methyl-1-propanal, 3-methyl-1-butanol, 3-methyl-1-butanal, acetone, acetoin, lactic, succinic and formic acid increased significantly within 48 h. Pyroglutamic and pyruvic acid decreased and then increased, while uric acid and sugars decreased within 96 h. Sodium benzoate, potassium sorbate or their combination extended the shelf-life of the control samples by four days. Pasteurization at 97C/10 min reduced the total mesophilic bacteria, lactic acid bacteria, yeasts and Enterobacteriaceae counts to nil and maintained the pH, titratable acidity, specific gravity, and total soluble content constant, and the products were mildly acceptable during storage for up to 60 days. Pasteurization alone was comparable to the combined effects of pasteurization and treatment with preservatives on the quality of the product. Pasteurization alone may therefore be appropriate for small-scale production and increased commercialization.     

ACTIVITIES OF CERTAIN AMINOTRANSFERASES AND NADP-DEPENDENT GLUTAMIC ACID DEHYDROGENASE IN YEAST DURING FERMENTATION

The activities of alanine (E.C.2.6.I.2.), aspartate (E.C.2.6.I.I) and glycine (E.C. 2.6.I.4) aminotransferases and NADP-dependent glutamic acid dehydrogenase (E.C.I.4.I.4) have been followed in Saccharomyces cerevisiae during fermentation in an all-malt wort. The synthesis of alanine aminotransferase is enough to furnish the yeast with alanine, but glycine aminotransferase activity is inadequate for glycine requirements during the fermentation period when glycine and alanine are not assimilated from the medium. The synthesis of all four enzymes is repressed to various extents during the early stages of fermentation, but de-repression occurs towards the end of the fermentation.     

猪肉自然发酵香肠中细菌和乳酸菌对生物胺积累的作用

在猪肉香肠的自然发酵时，检测了选择的污染菌对形成的生物胺的性质和产量的作用。本文主要研究的是在肉腐败过程中胺的变化和微生物生长的变化，而且重点研究的是加入产酪胺的短乳杆菌（L．brevis）和产尸胺的阴沟肠杆菌（E．cloacae）的猪肉发酵香肠在发酵时生物胺的积累。在腐败和香肠发酵时相关微生物和胺的量较多。尸胺的高度积累和大量的不理想肠细菌有关，在香肠发酵时，酪胺的产生并不完全是乳酸菌的作用。另一方面，也涉及到必要的生产香肠的自然发酵菌，污染菌对于腐胺和其它生物胺的作用，现在还不清楚。     

CHANGES IN SIZE OF GAS CELLS IN DOUGH AND BREAD DURING BREADMAKING AND CALCULATION OF CRITICAL SIZE OF GAS CELLS THAT EXPAND

Microscopic observation showed that a group of small air cells entrained during the early stage of mixing is the original cause of cell structure of bread. At the beginning of fermentation, about 3 × 10⁸/m² gas cells with diameters between 3 × 10⁻⁶ and 8 × 10⁻⁴ m were entrained in the dough. The distribution curve of cell size was approximately normal on a logarithmic scale. During fermentation and proofing, a great portion of carbon dioxide was released into cells larger than about 10⁻⁴ m in diameter that was equivalent to a few percentages of total number of gas cells. After baking, gas cells smaller than 10⁻⁴ m in diameter were not observed and the total number of cells in baked bread reduced to about 10⁶/m² with diameters between 10⁻⁴ and about 5 × 10⁻³ m. The critical cell size to expand generally agreed with the calculated value using an equation, rc'= 3s/E (re': critical radius to expand, s: surface tension, E: elasticity), and cited value of s and E.     

鲜食核桃贮藏中脂肪酶活性及油脂酸价变化

对贮藏中影响鲜食核桃脂肪酶活性与油脂酸价的因素进行了研究。发现贮藏温度、包装袋有无对脂肪酶活性影响显著（P〈0．05），缝合线紧密度对脂肪酶的活性影响不显著，贮藏温度、缝合线紧密度、包装袋有无对油脂酸价的影响显著（P〈0．05），核桃油脂酸价随着脂肪酶活性的增大而上升。     

冷藏鲜肉中腐败乳酸菌的分离及鉴定

利用稀释平板法从冷藏3 d的肉样品中共分离出60株疑似乳酸菌菌株,经过2次划线分离,然后进行革兰氏染色、镜栓、过氧化氢酶试验、明胶液化试验、硝酸盐还原试验和H2S检验,得到36株乳酸菌.将分离出的这36株乳酸菌,经过形态学和生理生化鉴定,确定他们属于5大类,即清酒乳杆菌,13株;马里乳杆菌,8株;消化乳杆菌,7株;口乳杆菌,4株;未知乳杆菌,4株.     

THE STRUCTURAL AND STORAGE CARBOHYDRATES OF SACCHAROMYCES CEREVISIAE: CHANGES DURING FERMENTATION OF WORT AND A ROLE FOR GLYCOGEN CATABOLISM IN LIPID BIOSYNTHESIS

Detailed analysis of the structural and storage carbohydrates of Saccharomyces cerevisiae (NCYC 240) during wort fermentation showed that there were no significant changes in the amounts of trehalose or alkali-soluble glycogen. However, glucan and mannan individually increased from ca4% of the yeast dry weight at pitching to ca6% during the first 3–17 h of fermentation, butthen declined to the former level. In the first 2 h of fermentation, prior to yeast multiplication, acid-soluble glycogen was rapidly dissimilated from ca 40% to ca 6% of the yeast dry weight. During this period of oxygen uptake, wort sugars were not removed by the yeast. Glycogen, therefore, was the sole source of metabolic energy for lipid resynthesis and hexose transport appeared to require the formation of a component membrane. During the latter phase of fermentation when the yeast was not growing but expending energy for maintenance of cellular functions, glycogen reserves were slowly depleted; after a period of prolonged anaerobic storage, the content of glycogen fell well below that which was initially present in the pitching yeast.     

OPTIMIZATION STUDY FOR THE PRODUCTION OF CITRIC AND GLUCONIC ACID FROM FIG WATER EXTRACT BY ASPERGILLUS NIGER IN SURFACE FERMENTATION

The production of citric and gluconic acid from fig extract by Aspergillus niger ATCC 10577 and A. niger B60 in surface fermentation was investigated. The strain 10577 gave higher concentration of citric and gluconic acid than strain B60. A maximum citric and gluconic acid concentration (20.5 and 97.0 g/L, respectively), citric acid yield (12%), biomass dry weight (18.5 g/L), and sugar utilization (85%) was achieved at an initial sugar concentration of 200 g/L and a pH of 7.0. On the other hand, the highest gluconic acid yield (79.7%) was obtained in culture grown at initial sugar concentration 100 g/L. The addition of 4% (v/v) methanol in the fig extract increased the concentration of citric and gluconic acid from 20.5 and 97.0 g/L to 30.7 and 145.5 g/L, respectively. Citric acid was separated from the gluconic acid by extraction with diethyl ether or ethyl acetate.