Journal of the Science of Food and Agriculture

Các phương pháp để phân tích định lượng anthocyanin, leuco‐anthocyanins, flavanol và tổng phenol trong chiết xuất mô thực vật được xem xét một cách có phê phán và các điều chỉnh phù hợp của các phương pháp hiện có được mô tả.

Phenolic secondary metabolites play an important role in plant‐derived food quality, as they affect quality characteristics such as appearance, flavour and health‐promoting properties. Their content in foods is affected by many factors that influence phenolic stability, biosynthesis and degradation. In terms of their biosynthesis the key enzyme phenylalanine ammonia‐lyase (PAL) is especially relevant, as it can be induced by different stress (environmental) conditions. In addition, polyphenol oxidases (PPO) and peroxidases (POD) are the main enzymes responsible for quality loss due to phenolic degradation. The different factors affecting phenolic‐related food quality are reviewed. These include internal (genetic) and environmental (agronomic) factors, technological treatments applied during postharvest storage of fruits and vegetables, as well as processing and storage of the processed products. The different strategies that are required to either maintain or enhance the phenolic‐related quality of foods are critically reviewed. Genetic modification designed to decrease polyphenol oxidases or peroxidases is not always a feasible method, owing to side problems related to the growth and defence of the plant. Agronomic treatments can be used to enhance the phenolic content and pigmentation of fruits and vegetables, although the information available on this topic is very scarce and even contradictory. Some postharvest treatments (cold storage, controlled or modified atmospheres, etc) can also improve phenolic‐related quality, as well as new processing methods such as irradiation (gamma, UV), high‐field electric pulses, high hydrostatic pressures and microwaves.

© 2001 Society of Chemical Industry

A rapid method is described for the colorimetric determination of 1.5–15 μg phytate phosphorus in concentrations as low as 3 μg ml⁻¹ in extracts of cereal grains and cereal products. The phytic acid is precipitated with an acidic iron‐III‐solution of known iron content. The decrease of iron in the supernatant is a measure for the phyticacid content.

This paper examines the nutritional and veterinary effects of tannins on ruminants and makes some comparisons with non‐ruminants. Tannin chemistry per se is not covered and readers are referred to several excellent reviews instead: (a) Okuda T et al. Heterocycles 30:1195–1218 (1990); (b) Ferreira D and Slade D. Nat Prod Rep 19:517–541 (2002); (c) Yoshida T et al. In Studies in Natural Product Chemistry. Elsevier Science, Amsterdam, pp. 395–453 (2000); (d) Khanbabaee K and van Ree T. Nat Prod Rep 18:641–649 (2001); (e) Okuda et al. Phytochemistry 55:513–529 (2000). The effects of tannins on rumen micro‐organisms are also not reviewed, as these have been addressed by others: (a) McSweeney CS et al. Anim Feed Sci Technol 91:83–93 (2001); (b) Smith AH and Mackie RI. Appl Environ Microbiol 70:1104–1115 (2004). This paper deals first with the nutritional effects of tannins in animal feeds, their qualitative and quantitative diversity, and the implications of tannin–protein complexation. It then summarises the known physiological and harmful effects and discusses the equivocal evidence of the bioavailability of tannins. Issues concerning tannin metabolism and systemic effects are also considered. Opportunities are presented on how to treat feeds with high tannin contents, and some lesser‐known but successful feeding strategies are highlighted. Recent research has explored the use of tannins for preventing animal deaths from bloat, for reducing intestinal parasites and for lowering gaseous ammonia and methane emissions. Finally, several tannin assays and a hypothesis are discussed that merit further investigation in order to assess their suitability for predicting animal responses. The aim is to provoke discussion and spur readers into new approaches. An attempt is made to synthesise the emerging information for relating tannin structures with their activities. Although many plants with high levels of tannins produce negative effects and require treatments, others are very useful animal feeds. Our ability to predict whether tannin‐containing feeds confer positive or negative effects will depend on interdisciplinary research between animal nutritionists and plant chemists. The elucidation of tannin structure–activity relationships presents exciting opportunities for future feeding strategies that will benefit ruminants and the environment within the contexts of extensive, semi‐intensive and some intensive agricultural systems. Copyright © 2006 Society of Chemical Industry

Cadmium (Cd) is a highly toxic heavy metal for both plants and animals. The presence of Cd in agricultural soils is of great concern regarding its entry into the food chain. Cadmium enters into the soil–plant environment mainly through anthropogenic activities. Compounds of Cd are more soluble than other heavy metals, so it is more available and readily taken up by plants and accumulates in different edible plant parts through which it enters the food chain. A number of approaches are being used to minimize the entry of Cd into the food chain. Proper plant nutrition is one of the good strategies to alleviate the damaging effects of Cd on plants and to avoid its entry into the food chain. Plant nutrients play a very important role in developing plant tolerance to Cd toxicity and thus, low Cd accumulation in different plant parts. In this report, the role of some macronutrients (nitrogen, phosphorus, sulfur and calcium), micronutrients (zinc, iron and manganese), and silicon (a beneficial nutrient) has been discussed in detail as to how these nutrients play their role in decreasing Cd uptake and accumulation in crop plants. Copyright © 2010 Society of Chemical Industry

Ethylphenols are important aromatic compounds of red wines. These compounds are formed in wines by some yeast species belonging to the genus Brettanomyces/Dekkera in the presence of hydroxycinnamic acids. These volatile phenols are responsible for the ‘phenolic’, ‘animal’ and ‘stable’ off‐odours found in certain red wines. The results presented show that the synthesis of the high quantities of ethylphenols found in the ‘phenolic’ red wines can occur during the ageing of wines having normally completed their alcoholic and malo‐lactic fermentations. This olfactory fault caused by Brettanomyces/Dekkera is found more frequently than the classical ‘mousy‐taint’ attributed to this yeast genus. In addition, the study of the mechanisms of biosynthesis of ethylphenols by Brettanomyces/Dekkera has shown the sequential activities of two enzymes. The first, is a cinnamate decarboxylase (CD), which assures the transformation of certain cinnamic acids into the correspondent vinylphenols; the second is a vinylphenol reductase, which catalyses the reduction of vinylphenols into ethylphenols. The CD activity of Brettanomyces/Dekkera is not inhibited by the polyphenolic compounds of red wines (procyanidins and catechins) while these compounds do inhibit the CD activity of Saccharomyces cerevisiae. On the other hand, the substrate specificities of the CD activities of Brettanomyces/Dekkera and Saccharomyces are different.

Isolated fresh beef muscles have been found to shorten more at 2° than at 37°. Minimum shortening occurs in the temperature region of 14–19°. At higher temperatures shortening coincides with the onset of rigor mortis but at low temperatures it begins rapidly and usually immediately. This shortening is reversible. Three different beef muscles show this effect but two rabbit muscles do not.

Fruits and vegetables are important sources of vitamins, minerals, dietary fiber, and antioxidants. The relative contribution of each commodity to human health and wellness depends upon its nutritive value and per capita consumption; the latter is greatly influenced by consumer preferences and degree of satisfaction from eating the fruit or vegetable. Flavor quality of fruits and vegetables is influenced by genetic, preharvest, harvesting, and postharvest factors. The longer the time between harvest and eating, the greater the losses of characteristic flavor (taste and aroma) and the development of off‐flavors in most fruits and vegetables. Postharvest life based on flavor and nutritional quality is shorter than that based on appearance and textural quality. Thus, it is essential that good flavor quality be emphasized in the future by selecting the best‐tasting genotypes to produce, by using an integrated crop management system and harvesting at the maturity or ripeness stage that will optimize eating quality at the time of consumption, and by using the postharvest handling procedures that will maintain optimal flavor and nutritional quality of fruits and vegetables between harvest and consumption. Copyright © 2008 Society of Chemical Industry

A rapid, simple test, complementary to the test for amylose content, was developed based on the consistency of a cold 4.4% milled‐rice paste in 0.20 N‐KOH. Consistency is measured by the length in a test tube of the cold gel held horizontally for 0.5 or 1 h. The consistency values are correlated with amylograph setback viscosity and can differentiate into three consistency types–low, medium, and high–even rice samples of similar amylose contents as long as they are between 24 to 30%.