P. Markakis

Anthocyanins and their stability in foods

The anthocyanin pigments are responsible for the red, blue, and purple color of most fruits and vegetables. This review covers the following aspects of anthocyanins: their chemical structure and the relation between chemical structure and color; the theories of their biogenesis and factors affecting their synthesis in plants; their distribution among fruits and vegetables; the chemical, physical, and biochemical factors affecting their degradation in fresh and processed food commodities; degradation schemes; ways and means for stabilizing these pigments in foods and methods for extracting, identifying, and quantifying their concentration in foods.

Cassava as a food

This review has attempted to examine information pertaining to the role of cassava (Manihot esculenta) as a major food source for a large part of the world population, particularly the countries of South America, Africa, and Asia, where it is primarily a major source of energy for 300 to 500 million people. Its cultivation, usually on small farms with little technology, is estimated to cover on an annual basis about 11 million hectares providing about 105 million tons, more than half of which is consumed by humans. The importance of cassava as an energy source can be seen by its growing demand in the European economic community countries where it forms up to 60% of the balanced diets for swine. Cassava is one of the crops that converts the greatest amount of solar energy into soluble carbohydrates per unit of area, thus 1 kg of moisture-free cassava meal may yield up to about 3750 kcal which would mean that a yearly production of 15 tons of cassava meal per hectare would yield some 56 million kcal. The major limitations of cassava as food appear to be its poor protein content and quality and the rapid post harvest deterioration of its roots which usually prevents their storage in the fresh state for more than a few days. However, in addition to its use for culinary purposes, cassava finds application in industrial products such as an adhesive for laundry purposes, for manufacturing paper, alcohol, butanol, dextrin, adhesive tape, textile sizing, and glue.

Lipid and other changes occurring during the fermentation and frying of tempeh

Abstract Three phases can be distinguished in the tempeh fermentation of soybeans with Rhizopus oligosporus . During the first phase a rapid increase in free fatty acid (FFA) content, number of bacteria and temperature is observed, along with a copious growth of the mould. The second phase is characterised by little or no change in FFA content, bacterial and mould growth and by a declining temperature. During the third phase the FFA development and bacterial growth recommence. Organoleptically, tempeh scores best at the end of the first phase ( 30 h at 32 ° C) and keeps its good quality during the second phase (one additional day at 32 ° C), but deteriorates rapidly during the third phase. Upon frying in coconut oil, tempeh undergoes a sharp reduction in FFA content with a concomitant increase in the FFA content of the frying oil. While frying alters the percentage composition of the glycerides of tempeh because of coconut oil absorption, the glyceride composition of the frying oil barely changes.

The effect of photoperiodism on the growth and the essential oil ofOcimum basilicum (Sweet Basil)

Ocimum basilicum var.citriodora plants were grown in July and August under 9 hours of daylight, outdoors, plus 0 to 15 hours of fluorescent light (125 fc), indoors. The overground portion of the plants was harvested when they were in bloom and subjected to Clevenger distillation. The essential oil was analyzed by gas chromatography and mass spectrometry. Flower development was most rapid when the plants were exposed to 18 hours of light daily. The greatest yield in herb was obtained under 24 hours of light; for photoperiods of 15 to 18 hours the yield was slightly lower, but the plants reached harvesting state 10 days earlier. The oil was resolved in 19 components, 8 of which were identified. The percentage of each of these components was affected differently by the photoperiods used in this experiment.

Estimation of potato protein content by dye binding

The protein content of 21 varieties of potatoes grown under similar conditions was measured by Kjeldahl nitrogen determination and by the binding of the dye orange G. A linear relationship between nitrogen content and bound dye was found. The regression equation Y=.105+.091X was derived, where Y was the absorbance of bound dye and X was the % total protein (% N x 6.25). The correlation coefficient was +0.9827 and the standard error of estimate was 0.07%.

α-Galactosidases of Vigna unguiculata

Abstract Three forms of α-galactosidase, I, II 1 and II 2 , were isolated from dormant cowpeas by means of gel filtration and ion exchange chromatography. Enzymes I, II 1 and II 2 exhibited optimum activity at pH 5.0, 5.9 and 5.3, respectively. The activation energies for the hydrolysis of p -nitrophenyl α- d -galactoside (PNPG) were 5.1, 3.5 and 3.3 kcal/mol for enzymes I, II 1 and II 2 , respectively. The M r s were ca 111 000, 29 000 and 30 000, respectively. Two column chromatographic separations and SDS- PAGE indicated that enzyme I is a tetramer of enzyme II 2 . The K m and V max values of the three enzymes were different for one artificial and two natural substrates. The enzymes also differed in their stabilities during storage for 24 hr at four different temperatures and various pH values.

Properties of ascorbate oxidase isozymes

Abstract The ascorbate oxidase of two squash cultivars was resolved into five molecular forms by gel electrophoresis; that of cucumber was resolved into three forms. Molecular weight estimates by Sephadex gel filtration and interconversions of these forms strongly suggest the presence of a monomeric form of MW 30 000 for the cucumber enzyme and 35 000 for that of the squashes. The other two forms in the cucumber appear to be a dimer and a tetramer, whilst a tetramer, an octamer, a dodecamer, and a polymer of MW between 670 000 and 2 000 000 are likely to be the other four forms present in the squashes. The monomer was the most abundant form in the cucumber and the tetramer in the two squashes. The peel of these fruits was higher in activity than the flesh, but the isozyme pattern was the same in peel and flesh. The tetramer of the squashes and the dimer of cucumbers were the most resistant forms to heat inactivation. The enzyme is soluble and not associated with subcellular particles.

Blue-green algae as a source of protein

Abstract Anabaena flos-aquae, an N-fixing and photosynthesising blue-green alga, was grown in defined liquid media. Although this organism grew well in autotrophic solution, it rendered a higher yield in a medium containing 1% glucose. A good procedure for extracting the protein from the cells was heating them in 3 n HCl at 95°C for 10 min, adjusting the pH to 11 with 3 n NaOH after cooling, letting them stand at room temperature for 1h, centrifuging out the debris and exposing the supernatant to 15,000 international lux of fluorescent lamp light for 10h. The treated solution contained 80% of the nitrogen of the cells and it had a pale yellow colour. The protein of the solution was further fractionated into a pH-4-insoluble fraction and an acetone-insoluble fraction. Both fractions were easily digested by pepsin in vitro and were deficient in sulphur-containing amino acids. The amino acid scores of the fractions were 74 and 60, respectively.

Ascorbate oxidase isozymes

The ascorbate oxidase of yellow summer squash (Cucurbita pepo condensa) was separated into five isozymes by polyacrylamide gel electrophoresis. One of the forms accounted for 70 per cent of the recovered total enzymic activity. A reversible association-dissociation occurs in the isozymes as a result of changes in ionic concentration.

Changes in alpha-galactosidase activity and oligosaccharides during germination and incubation of cowpeas (Vigna unguiculata)

Abstract Germination of cowpeas at 24 and 30°C resulted in increased alpha-galactosidase activity during the first 6 to 12 h and leveled off subsequently. Stachyose content declined by 38% during 12 h of germination at 24°C. Incubation of a cowpea flour paste for 24 h at 24°C resulted in a large reduction of the stachyose and sucrose concentrations, and in their practical elimination at 34°C. Incubation for 12 h at 24 and 34°C of a cowpea paste made from 6-h germinated seeds resulted in a large decrease in stachyose content. Incubation of flour or germination of seeds effectively reduced the stachyose concentration of cowpeas.