Seasonal clonal variations and effects of stresses on quality chemicals and prephenate dehydratase enzyme activity in tea (<Emphasis Type="Italic">Camellia sinensis</Emphasis>)

Seasonal and clonal variations in catechins, flavour component 2-phenylethanol and prephenate dehydratase (PDT) enzyme were studied in tea clones representing both Assam and China varieties growing in Kangra region of India. Catechins were analysed and quantified by HPLC, and 2-Phenylethanol was quantified by GC. Assam variety recorded higher amounts of catechins and PDT activity than China variety in all the three growth flushes. Activity of PDT and catechins content was high during mains growth flush followed by early and backend flush. 2-Phenylethanol content recorded higher levels in China variety compared to Assam variety, and higher content was observed in the early flush and decreased thereafter with progress in season in both the varieties. Decrease in catechins content, 2-phenylethanol and PDT activity was observed in the tea shoots infested by Exobasidium vexans over healthy shoots. Drought stress induced by withholding water for a period of 8 days caused initial increase in the contents of the catechins, 2-phenyethanol and PDT activity and decreased with 3 day onwards with an increase in the severity of water stress. Seasonal variations showed modulations in catechins and 2-phenylethanol in response to changing environmental conditions, suggesting that depending on the season there is higher flux of substrate towards the required product.     

Seasonal and clonal variations in some major glycosidic bound volatiles in Kangra tea (Camellia sinensis (L.) O. Kuntze)

Seasonal and clonal variations in glycosidic bound volatile compounds were studied in tea clones representing the three different varieties viz. sinensis, assamica and cambodiensis grown in Kangra region. Glycosidic bound volatile compounds were characterised by GC–MS and quantification of major volatiles was done by GC. (E)-2-hexenal, benzyl alcohol, phenylethanol, linalool, linalool oxides, geraniol and methyl salicylate were the major glycosidic bound volatiles identified in tea shoot. Clonal variations in the quantity were observed in these bound volatiles. Seasonal variations were also observed in the quantity of bound volatiles in regional Kangra clone during three different growth flushes of tea. These variations in glycosidic precursors of volatile compounds were studied in context with orthodox made tea and its quality. These seasonal and clonal variations in precursors of volatile compounds can be directly correlated to the difference in the quality of tea made from these cultivars.     

Seasonal variations in theaflavins,thearubigins, total colour and brightness of Kangra orthodox tea (Camellia sinensis (L) O Kuntze) in Himachal Pradesh

Variations in theaflavins, thearubigins, total colour and brightness of orthodox black tea were studied for four consecutive years (1993–1996) with a view to evaluating the effects of changing weather conditions on the quality of Kangra tea. A degree of withering of 600–650 mg g⁻¹ during the first, second and fourth seasons was optimal for the development of significantly higher brightness and total colour characteristics. The quality of rainy season teas suffered owing to high chlorophyll content and low degree of withering. Hot air circulation through the withering troughs to assist evaporation of leaf moisture increased the brightness and total colour of rainy season teas. High atmospheric demand during the dry season assisted loss of green leaf moisture, but withering and brightness exhibited significant negative correlations with high relative humidity and rainfall. Summer season teas were superior in their total colour and brightness. © 2000 Society of Chemical Industry     

Effects of potassium and magnesium nutrition on the quality components of different types of tea

In field experiments, the effects of potassium and magnesium nutrition on the quality components of different types of tea, including black tea, oolong tea and green tea, were studied. The results show that K and Mg fertilizer application increased the contents of free amino acids and caffeine of the various tea types with the maximum increase found in the treatment including both nutrients. The content of polyphenols in tea leaves was also increased by K application. The effect of Mg on polyphenol content was inconsistent. In general, Mg apparently decreased the content of polyphenols and only in case the soils were depleted of plant available K and Mg, a slight increase could be observed. The contents of theaflavins and thearubigins, important quality components of brewed black tea, were also increased by K application. Flavour compounds in brewed oolong tea were considerably improved by K and Mg application. © 1999 Society of Chemical Industry     

高压脉冲电场对牛奶中风味物质的影响

本实验采用SPME-GC-MS 联用的方法,对鲜牛乳、UHT 灭菌牛奶和高压脉冲电场(PEF)处理(35kV/cm,400μS,200Hz)牛乳的风味成分进行分析。从鲜牛乳、UHT 灭菌乳和PEF 处理乳分别鉴定出19、17、18 种主要挥发性化合物。通过对不同处理方式牛乳挥发性风味成分的比较研究,PEF 处理较UHT 处理对牛乳中风味物质影响较小,且产生较少的与蒸煮味相关的含硫化合物。     

发酵香肠风味物质研究现状

发酵香肠的风味物质主要来自于碳水化合物、脂肪、蛋白质的代谢和氧化，以及人为添加的香辛料。本文概述了现已鉴定的发酵香肠的主要风味物质及来源的研究情况。     

Shelf life of shrimp (Penaeus merguiensis) stored in ice (0°C) and partially frozen (—3°C)

Sensory, biochemical and microbiological changes and changes in SDS-PA GE patterns of myofibrillar and sarcoplasmic proteins were studied in shrimp (Penaeus merguiensis) muscle during storage at partial freezing temperature (—3°C; PFS) and in ice (0°C; IS). During PFS up to 20 days there were slight changes in biochemical parameters, apparently no changes in microbiological populations, and no changes in electrophoretic protein patterns. Rapid changes in these parameters occurred in IS over the same period. Sensory assessment of shrimps stored at PFS showed that a considerable increase in prime quality life was possible at this temperature over shrimps in IS. Prime quality life of shrimps in PFS was found to be 16 days, compared with 8 days in IS. Extension of prime quality life was attributed to the significantly slower rate of biochemical and microbiological changes at PFS compared with IS. Changes in sensory properties were associated with changes in some of the chemical properties.     

Predictive models for bacterial growth in sea bass (Dicentrarchus labrax) stored in ice

The purpose of this paper was to estimate microbial growth through predictive modelling as a key element in determining the quantitative microbiological contamination of sea bass stored in ice and cultivated in different seasons of the year. In the present study, two different statistical models were used to analyse changes in microbial growth in whole, ungutted sea bass (Dicentrarchus labrax) stored in ice. The total counts of aerobic mesophilic and psychrotrophic bacteria, Pseudomonas sp., Aeromonas sp., Shewanella putrefaciens, Enterobacteriaceae, sulphide‐reducing Clostridium and Photobacterium phosphoreum were determined in muscle, skin and gills over an 18‐day period using traditional methods and evaluating the seasonal effect. The results showed that specific spoilage bacteria (SSB) were dominant in all tissues analysed, but were mainly found in the gills. Predictive modelling showed a seasonal effect among the fish analysed. The application of these models can contribute to the improvement of food safety control by improving knowledge of the microorganisms responsible for the spoilage and deterioration of sea bass.     

Oil quality characteristics and headspace volatiles of newly released groundnut (Arachis hypogaea L) cultivars

Several groundnut (Arachis hypogaea L) cultivars developed by the International Crops Research Institute for the Semi-arid Tropics (ICRISAT), and one local cultivar for use as a control were grown in the post-rainy and rainy seasons at Patancheru, India. Free and bound lipids were extracted and their fatty acid compositions determined. Acid, peroxide, iodine and saponification values were determined. Flavour quality was evaluated using headspace analysis. The quantity of total lipids was significantly higher in the cultivars grown in the rainy season than those grown in the post-rainy season and was higher in the ICRISAT cultivars than in the control in both seasons. Oleic (O) to linoleic (L) acid ratio was lowest in the chioroform-methanol extract and highest in water-saturated butanol extract. One ICRISAT line, ICGS 21, showed the highest O/L ratio in all lipid fractions in both seasons. Among the flavour components, n-methyl pyrrole, associated with an objectionable musty flavour, was present in very high concentration in all the cultivars.     

Occurrence and distribution of lipoxygenase in Camellia sinensis (L) O Kuntze and their changes during CTC black tea manufacture under southern Indian conditions

The optimal activity of tea lipoxygenase was found to be at pH 7·5 and 9·0, indicating the presence of two types of isoenzymes. Tea lipoxygenase was inhibited by cyanide and a small fraction appeared to be quite heat stable. Clonal and seasonal variations in lipoxygenase activity was significant. An increase in lipoxygenase activity was observed with leaf maturity. The lipoxygenase activity decreases with age from pruning and increases with an increase in plucking interval. The changes of lipoxygenase activity during CTC manufacture revealed that it increased with the degree of withering and upon rolling. However, a gradual decline was recorded during the fermentation and drying processes. The residual lipoxygenase activity in black tea is expected to affect its quality on storage. © 1998 Society of Chemical Industry.     

Quality evaluation of black CTC teas based upon seasonal variations

Effects of seasonal variations on the colour and chemical constituents of Indian black tea were investigated. The experimentation involved collection of different black tea samples that were cultivated at the same tea garden but harvested in three different seasons. Measurement of moisture content was done along with theaflavins (TFs), thearubigins (TRs) and colour (CIE La*b* values) of the brewed tea liquor using spectrophotometric approach. The correlation analysis between chemical constituents, that is, TFs and TRs, moisture content, colour and quality grading was done by using principal component analysis (PCA). The results suggest that quality of tea is dependent upon seasonal variations in terms of chemical changes such as TFs, TRs and moisture content, which also correlate well with colour. The efficacy of the colour of brewed tea liquor in explaining the changes in tea quality due to seasonal variations can be beneficial for scientific fixation of prices at tea auction centres.     

Calcium chloride irrigation influence on yield,calcium content,quality and shelf‐life of the white mushroom Agaricus bisporus

Seven CaCl₂ irrigation treatments (0.15, 0.25, 0.35, 0.45, 0.55, 0.75 and 1.00%) were applied to the Agaricus bisporus white strain A15 (Sylvan) in order to evaluate, in comparison with the water‐irrigated crop, their effect on production characteristics, ie yield, sporophore number and size mix, average mushroom weight as well as pileus and stipe Ca content. In addition, initial mushroom colour and texture in three successive flushes and their variations during post‐harvest storage for 8 days at 4 °C and for 2 days at 18 °C were determined. Statistical analysis of data revealed that crop yields were not affected by the individual treatments, whereas the mushroom number was reduced and the average sporophore weight was enhanced. A strong positive correlation was established between CaCl₂ dosage and Ca content of fresh mushrooms, which increased considerably in the third flush by accumulating in both pileus and stipe parts (the former containing less Ca than the latter) and presented a maximum for the 0.75 and 1.00% CaCl₂ treatments. At harvest, colour of second‐ and third‐break mushrooms was significantly improved by all CaCl₂ treatments. This beneficial effect was more pronounced after 8 days of cold storage and during shelf‐life in sporophores treated with 0.35, 0.75 and 1.00% CaCl₂. No consistent correlation was found between Ca content and texture of fresh and stored mushrooms. However, although softer mushrooms were recorded at harvest in most CaCl₂‐irrigated crops, 0.25, 0.75 and 1.00% concentrations appeared to retard mushroom softening, promoting firmness at the 8th day of cold storage and during shelf‐life. © 2001 Society of Chemical Industry     

Effects of seasonal variations on the quality of set yogurt,stirred yogurt,and Greek-style yogurt

We studied the effects of seasonal variations on the quality of stirred yogurt, set yogurt, and Greek-style yogurt over 2 milking seasons in New Zealand. Correlations between the properties of the yogurts, the characteristics of the milk, and the acid gelation properties induced by glucono-δ-lactone, reported in our previous works, were also explored. Set yogurt and Greek-style yogurt from the early season had the highest firmness over the seasons. The yogurt firmness correlated with the gel strength of glucono-δ-lactone-induced acid gels, indicating that the latter could, to some extent, predict the seasonal variations in the firmness of set yogurt. The correlation studies highlighted the potentially important role of the glycosylation of κ-casein in the seasonal variations in the yogurt structures. Yogurt made from mid-season milk had the lowest water-holding capacity, which may have played a part in lowering its firmness and viscosity. Late-season stirred yogurt displayed the strongest resistance to shear-induced thinning, which might arise from the unique viscoelastic properties of late-season yogurt gels.     

Abundance of Plodia interpunctella (Hübner) and Cadra cautella (Walker) infesting maize stored on South Carolina farms: seasonal and non-seasonal variation

Seasonal trends and short-term fluctuations in abundance of Plodia interpunctella (Hübner) and Cadra cautella (Walker) infesting maize stored on two South Carolina farms were studied during three storage seasons (September 1990–June 1993). Coils of corrugated paper placed on the grain surface were used to trap mature larvae seeking pupation sites. Temperatures in the grain (18-cm-deep) and in the bin headspace were recorded hourly, and grain moisture content was measured weekly. Weekly mean numbers of moth larvae, and adults of two natural enemies, trapped in the coils were used for tracking changes in their abundance over time. The most significant findings were: (1) a seasonal pattern of abundance in both moth species that persisted from farm to farm and year to year, and (2) the coincidence of the highest population levels with the lowest temperatures. With few exceptions, the moth populations increased in the fall, reached their highest levels in winter, and then declined to low levels by early spring. The persistence of this pattern suggests a seasonal regulatory mechanism, with onset of low temperature as the primary initiator of population decline and adversely high temperature as a contributor to its protraction through spring into early summer. This view is supported by our observations of temperature and moth abundance, in conjunction with published information on the biological limitations of the two species. However, other factors, such as predators, parasitoids, and viral infection, may have contributed to the final population collapse. Superimposed upon the seasonal trends were short-term, non-seasonal cycles of abundance with variable periods. Population theory suggests that predation, parasitism, disease, and competition may have produced these cycles.     

Liquid Loss as Effected by Post mortem Ultrastructural Changes in Fish Muscle: Cod (Gadus morhuaL) and Salmon (Salmo salar)

This study was performed in order to assess the effect of early post mortem structural changes in the muscle upon the liquid-holding capacity of wild cod, net-pen-fed cod (fed cod) and farmed salmon. The liquid-holding capacity was measured by a low speed centrifugation test. Transmission electron microscopy was used to discover ultrastructural changes both in the connective tissue and in the myofibrils. Differential scanning calorimetric thermograms of the muscle proteins were recorded to elucidate whether fundamental differences did exist between the proteins of the raw material tested. Multivariate statistics were used to explicate the main tendencies of variations in the thermograms. The salmon muscle possessed much better liquid-holding properties than the cod muscle, and wild cod better than fed cod regardless of the storage time. Both fed cod and farmed salmon, underwent the most severe structural alterations, probably caused by the low muscle pH values. The higher liquid-holding capacity of the salmon muscle was related to species specific structural features and better stability of the muscle proteins. The myofibrils of the salmon muscle were denser and intra- and extracellular spaces were filled by fat and a granulated material. The differences in thermograms of muscle from wild and fed cod were largely explained by the variations in pH. The severe liquid loss of fed cod is due to a low pH induced denaturation and shrinkage of the myofibrils. Post mortem degradation of the endomysial layer and the sarcolemma may have further facilitated the release of liquid.     

Effects of season on proximate and fatty acid compositions of two mediterranean fish – the round herring (Etrumeus teres) and tub gurnard (Chelidonichthys lucernus)

The aim of this work was to study the seasonal variation of the proximate and fatty acid compositions in the round herring (Etrumeus teres) and tub gurnard (Chelidonichthys lucernus) caught from the North‐Eastern Mediterranean Sea. Proximate compositions and fatty acid contents of both fish species showed statistically significant seasonal variations (P < 0.05). While the protein contents were at its highest in winter, the lipid contents were at its highest in autumn. The main fatty acids were C16:0 (palmitic acid), C18:0 (stearic acid), C16:1 n‐7 (palmiteoleic acid), 18:1 n‐9c (oleic acid), C20:5 n‐3 (eicosapentaenoic acid) and C22:6 n‐3 (docosahexaenoic acid). The total polyunsaturated fatty acid in round herring was highest in winter, whereas that in tub gurnard was highest in spring.     

Gilthead seabream (Sparus aurata): suitability for freezing and commercial alternatives

The quality of portion‐size farmed gilthead seabream (Sparus aurata) during frozen storage and the influence of post‐mortem treatments were studied in order to find new ways of marketing this species. Portion‐sized gilthead seabream, fasted for 48 h prior to slaughter, were frozen and stored at ?20 °C for up to one year. Whole fish were frozen immediately after rigor mortis; gutted fish were frozen immediately after rigor and after 5 days of storage in ice. All lots were stored at ?20 °C for up to one year. The myofibrillar protein of this species was very stable and a slight decrease of solubility in salt solutions was found only after one year of frozen storage. A slight decrease in water‐holding capacity and a slight increase in shear strength were observed, but these were lower than in other species. These changes were reflected as increased toughness and reduced juiciness in sensory analysis of the cooked fillets after one year. The main changes in the cooked fillets were observed in odour and flavour. No significant detrimental effect due to the guts was detected during frozen storage. Storage in ice prior to freezing was reflected in sensory assessment of the raw fish, mainly in terms of initial higher demerit points for fishy odour, gills and eyes; however, no effect was observed in the cooked fillets. Copyright © 2004 Society of Chemical Industry     

Determination of nutrients and volatile constituents of Agaricus bisporus (brown) at different stages

BACKGROUND: The physical properties, proximate composition, mineral and vitamin contents, and estimated volatile components of Portobello mushroom, Agaricus bisporus (brown), were analyzed in three flushes and at two different harvest times. The results showed different trends in the flushes and harvest terms studied. RESULTS: The mean values of texture, diameter, and protein of the harvested produce were 1.78–1.97 kg mm^?2, 4.67–5.02 cm, and 4.18–3.31% wet weight basis (wb), respectively. The mean Zn, Fe, P, Mg, K, Na, and Ca contents of both harvests (mg kg^?1 wb) were 8.15–7.07, 7.40–7.96, 1180.93–1038.69, 88.05–76.29, 213.29–238.82, 2652.0–2500.89, and 534.2–554.80, respectively. In terms of vitamin C, folic acid, thiamin, riboflavin, and niacin, the mean contents (mg kg^?1 wb) were 6.75–3.97, 0.09–0.08, 0.085–0.09, 0.27–0.29, and 3.62–2.94, respectively. The estimated volatile components comprised 18‐ or 16‐carbon compounds such as octadecanoic acid, hexadecanoic acid derivatives, and other important volatiles like dl‐limonene, n‐nonane, benzendicarboxylic acid, and cis‐linoleic acid esters. CONCLUSION: Nutritive contents and estimated volatiles of Portobello mushroom were evaluated in detail at different stages. Copyright © 2009 Society of Chemical Industry     

Characteristics of mince from pond-bred silvercarp (Hypophthalmichthys molitrix) and preliminary experiments on its use in sausages

The quality of fresh, chilled and frozen mince made from the flesh of pond-bred silvercarp (Hypophthalmichthys molitrix (Val)) was evaluated. Flavour panel scores for all minces were acceptable and this quality did not deteriorate during storage for one week in a domestic refrigerator (5–6°C) or for one year at ?20°C. The levels of oxidative rancidity (2-thiobarbituric acid analysis) in the minces were consistent with this maintenance of quality. Aerobic plate counts at 25°C of fresh mince rose from 7–9 × 10⁴ to 1.1 × 10⁵ after 6 days' storage at 5–6°C. Coliform and psychrotroph counts rose from 1.0 × 10¹ and 7–8 × 10³ to 5–4 × 10² and 1.3 × 10⁴, respectively. The functional and textural properties of pond-bred silvercarp mince in terms of salt-soluble protein content, water binding capacity and penetrometer values were measured on fresh, refrigerated and frozen samples. All-fish sausages and frankfurters developed from pond-bred silvercarp mince were assessed in laboratory and consumer tests against commercial beef sausages and frankfurters. The fish products competed well and achieved levels of acceptance similar to those of the beef-containing products. Texture measurements revealed slight changes in the fish products during storage for 7 days at 5–6°C. No spoilage was detected in any of the products after a week at 5–6°C. The nutritional advantages of the fish sausages and frankfurters are discussed.