O. T. de Villiers

Role of pectolytic enzymes in the development of woolliness in peaches

SummaryThe role of pectolytic enzymes in the development of woolliness in peaches (Prunus persica, cv. Peregrine), stored at different temperatures, was studied. All peaches became woolly during a ripening period of 12 days at 10°C following storage at 2°C, whereas 75% of those stored at –0.6°C developed this disorder. Only 6% of fruit showed symptoms of woolliness after 48 h at 23°C prior to storage. The sugar content, as well as the viscosity of soluble pectin, of peaches stored after the delay period reached a maximum during the 15th day of cold storage, after which it decreased until the end of the ripening period. In peaches stored immediately, however, the maximum sugar content and viscosity was reached during the ripening period. Pectinesterase (PE) activity fluctuated between the different treatments and its possible role in the development of woolliness is not clear. The polygalacturonase (PG) activity of those peaches which became woolly after being stored directly at either temperature was mark...

Physiological changes associated with the development of woolliness in ‘Peregrine’ peaches during low-temperature storage

SummaryThe effects of different durations of storage and temperature on the development of woolliness in peaches (Prunus persica cv. Peregrine) were studied. All peaches became woolly during ripening for 12 days at 10°C following storage at 2°C but only 75% of those stored at –0.6°C developed this disorder. Firmness and the respiration rate of woolly peaches decreased sharply at the onset of woolliness while peaches which subsequently became woolly had a lower ethylene content throughout the storage and ripening periods. When peaches were held for 2 days at 23°C before storage at either temperatures, few fruit developed symptoms of woolliness. Although the amount of extractable juice remained high in fruit stored without pre-treatment at 23°C, the quantity fell rapidly during the ripening of peaches which became woolly.

Multivariate assessment of environmental effects on hard red winter wheat. I. Principal-components analysis of yield and bread-making characteristics

The attributes of yield and bread-making quality of winter wheats produced in the Free State are subject to environmental effects. The result is a supply to the baking industry of flour of inconsistent quality, which in turn is detrimental to the market value of wheat. Various genetic and environmental factors may affect bread-making quality. In the first part of this study we demonstrated the magnitude of environmental and genetic factors, and used principal-components analysis to examine the underlying source of variability in the bread-making quality of winter wheat cultivars. Yield and protein concentration responded to environmental influences, whereas the dough-mixing requirement was primarily inherently determined. Variation in protein concentration accounted for variation in the mixing requirement of one cultivar and the SDS sedimentation volume of most cultivars.

Effect of time of examination and ripening temperature on the degree of woolliness in nectarines

SummaryNectarines (Prunus persica, cv. Independence) were stored at –0.5°C for four weeks immediately after harvest. After cold storage the fruit was ripened at 10, 15 or 20°C. The percentage woolly fruit, ripened at 10 and 20°C, initially increased until all fruit became woolly (at 15°C, only 92% of the fruit became woolly) and thereafter decreased until no woolliness was observed. The rate of increase and decrease in woolliness depended on the ripening temperature. Fruit softened by 3.9 N during the four weeks of cold storage. The firmness of fruit at the three ripening temperatures decreased linearly to a minimum of about 24 N. The rate of softening depended on the ripening temperature. The highest degree of woolliness at the three ripening temperatures occurred when the firmness varied between 29 and 34 N. The percentage of extractable juice decreased during ripening to a minimum value (concomitant with the highest percentage of woolly fruit) and increased again thereafter.

The Effect of Partial Defoliation on Quality Characteristics of Vitis vinifera L. cv. Cabernet Sauvignon Grapes 1. Sugars, Acids and pH

The effect was studied of partial defoliation (33% and 66%) on the sugar and acid accumulation and pH in grapes of Vitis vinifera L. cv. Cabernet Sauvignon. Although the total soluble sugar (TSS) in grapes of partially defoliated vines was significantly higher than that of non-defoliated vines in some cases, no significant differences were generally found. No significant differences in total titratable acidity (TT A) were found between treatments. The timing of defoliation had no effect on TSS in grapes, whereas TT A tended to be higher the earlier partial defoliation was commenced. In general, 33 % and 66% defoliated vines respectively produced approximately 33 % and 200% more TSS and TT A in the fruit per cm2 leaf area than non-defoliated vines. No significant differences between defoliation treatments were found on a per gram dry berry mass or per berry basis for glucose and fructose or tartaric and malic acid. However, 66% defoliated vines had significantly less soluble solids in berries per shoot, which was probably caused by a lower total berry mass per shoot. Although no significant differences in sugar composition could be found between defoliation treatments, tartaric acid levels tended to be higher and malic acid levels lower as a result of partial defoliation. Partial defoliation had no effect on the accumulation patterns of sugars and acids. Glucose dominated in berries at veraison, with fructose dominating at ripeness. The highest total tartaric and malic acid concentrations occurred at pea size. Malic acid content decreased rapidly from veraison, whereas the decrease in tartaric acid was not pronounced. Must pH was not affected by partial defoliation. The results seem to suggest that the general metabolism of vines was favourably changed by partial defoliation, mainly in terms of a more favourable source: sink ratio, more efficient photosynthesis, and an improved canopy microclimate.

The effects of storage temperature and fruit size on firmness, extractable juice, woolliness and browning in two nectarine cultivars

Fruit firmness, extractable juice, woolliness and browning of the mesocarp tissue in ‘Independence’ and ‘Flavortop’ nectarines stored at —0.5°, 3°, 5° and 7°C for four weeks were determined during ripening at 15°C. The firmness of both ‘Independence’ and ‘Flavortop’ during ripening decreased as storage temperatures increased. The percentage extractable juice after cold storage and during ripening varied considerably between cultivars and between the storage temperatures. The extractable juice of fruit stored at higher temperatures tended to increase during ripening, whereas fruit stored at lower temperatures tended to decrease first before increasing. At storage temperatures of —0.5° and 3°C both cultivars passed through a stage of woolliness during ripening, while less woolliness occurred after storage at 5° and 7°C. In both cultivars the percentage extractable juice during ripening was higher on average at storage temperatures of 5° and 7°C. Severe browning of mesocarp tissue in both cultivars occurred ...

Evaluation of proline accumulation as an indicator of drought tolerance in spring wheat cultivars

The aim of this study was to evaluate proline accumulation as an indicator of drought stress and drought tolerance in spring wheat cultivars (Triticum aestivum L.) grown in the Western Cape. Drought stress was induced in whole plants and leaf discs in two cultivars with known drought tolerance, namely, Gamtoos (drought tolerant) and S ST 66 (slightly drought sensitive), as well as in two cultivars with unknown drought tolerance, namely, Nantes and SST 44. To assess the effect of growth stage on the reaction of the cultivars to drought stress, stress was induced during pre-anthesis and also during anthesis. Proline accumulation in whole plants showed clear genotypical differences during pre-anthesis and, to a lesser extent, during anthesis. A positive correlation between the degree (onset and extent) of proline accumulation and drought tolerance was found for Gamtoos and SST 66. Proline accumulation patterns in leaf discs did not correlate with results obtained with whole plants.

EFFECT OF TEMPERATURE MANIPULATION DURING STORAGE AND RIPENING ON FIRMNESS, EXTRACTABLE JUICE AND WOOLLINESS IN NECTARINES

‘Independence’ nectarines were stored at — 0.5°C for three or four weeks or at 3°C for four weeks or kept at room temperature for 18 h prior to storage for four weeks at -0.5°C. After cold storage, fruit from all treatments was ripened at 10°, 15°or20°C. In all treatments the percentage woolly fruit initially increased to high values and thereafter decreased with further ripening. The rate of increase and decrease in woolliness depended on the ripening temperature. A storage period of four weeks at — 0.5°C resulted more woolliness during subsequent ripening. Woolliness persisted longer after a four-week cold storage period than after a three-week one. When fruit was delayed at room temperature prior to cold storage, woolliness generally developed earlier and to a lesser extent during ripening. At all ripening temperatures initial storage at 3°C resulted in most woolliness extending over the longest period. In addition, browning of the meso- carp tissue occurred only in fruit cold stored at 3°C.-The delay ...

Barley cultivar identification by acid Polyacrylamide gel electrophoresis of hordein proteins

Methods are described for the extraction and separation of hordein proteins of barley by acid Polyacrylamide gel electrophoresis as a means of identifying different cultivars. Experimental conditions for the extraction of the proteins from single kernels and from corresponding flour samples are described as well as the use of different solvents for extracting the hordein proteins. An electrophoretic formula was prepared for each cultivar using relative band mobility and staining intensity of protein bands. The resulting band patterns were used to identify different cultivars. Single kernels and flour samples gave identical band patterns but the intensity of bands of kernels was generally more pronounced.

Use of the SDSS test to predict the protein content and bread volume of wheat cultivars

The relationship between the sodium dodecyl sulphate sedimentation volume (SDSS test) and the protein content and bread volume of wheat cultivars was determined to ascertain whether the SDSS test could be used to predict these parameters of baking quality. This test proved to be a good indication of baking quality as the SDS sedimentation volumes were positively correlated with both protein content and bread volume of the cultivars. Nitrogen fertilization affected the SDS sedimentation volume as well as the protein content and bread volume, thereby affecting the relationship between these parameters. Higher correlation coefficients between the different parameters were found at higher nitrogen applications. Some of the correlation coefficients were affected by the locality where the wheat was grown.