D. E. Irving

Respiration, soluble carbohydrates and enzymes of carbohydrate metabolism in tips of harvested asparagus spears

We held asparagus (Asparagus officinalis L.) spears at 20°C for up to 5 days after harvest and examined changes in respiration rate, soluble carbohydrates and the activities of enzymes concerned with glycolysis and carbohydrate breakdwon in the tips. Respiration rate declined after harvest, to reach 25% of its initial rate after 2 days. The gas exchange (respiratory) quotient was 1.05 at harvest and declined in parallel with respiration rate for 2 days. There was a rapid loss of sucrose from spear tips over the first 6 h, and a more gradual loss after that. Glucose concentration declined gradually throughout, but fructose concentration barely changed over 3 days. We conclude that a major change in the metabolism of asparagus spear tips occurs soon after harvest. The change is characterised by a switch from sucrose-derived hexose phosphate to another primary respiratory substrate, probably derived from protein and/or lipid. The activities of hexokinase (EC 2.7.1.1), fructokinase (EC 2.7.1.4), phosphofructikinase (EC 2.7.1.11), sucrose synthase (EC 2.4.1.13) and alkaline invertase (EC 3.2.1.26) were generally low compared with the activities of the other enzymes assayed. Overall, enzyme activities declined over 5 days of starvation. The exceptions were hexokinase, phosphofructokinase and pyruvate kinase (EC 2.7.1.40), where activities were reasonably steady.

Sugars and sweetness in buttercup squash

Sweetness is an important attribute in the flavour, acceptability, and perceived quality of winter squash. Glucose, fructose and sucrose contributed differently to the perceived sweetness of eight winter squash cultivars (Cucurbita maxima) rated by a trained sensory panel. Sucrose was the most important sugar in predicting sweetness, but better predictions were obtained using additional combinations of glucose and fructose content. Sugar content and relative proportions of glucose, fructose and sucrose changed during storage. Starch content decreased for all cultivars during storage, and was an important predictor of sweetness for high starch cultivars only. When data for sweetness were regressed against sugar concentrations, adjusted R2 values in the range of 0.68-0.89 were obtained for seven of the cultivars. Including starch in the regression models unproved the adjusted R2 values to 0.77-0.94.

Changes in sugar, protein, respiration, and ethylene in developing and harvested Geraldton waxflower (Chamelaucium uncinatum) flowers

Abstract Sugar and protein levels and rates of respiration and ethylene production were measured for Geraldton waxflower (Chamelaucium uncinatum) flowers in order to characterise flower development and senescence in this cut flower crop. Ten sequential stages of floral development were identified. Sugar levels increased during bud development, the highest concentrations (c. 130 mg sucrose equivalents/g dry weight (DW) being measured during the nectiferous stages of flower opening. There was little variation in either soluble or insoluble protein levels during flower development, levels averaging around 19 and 25 mg bovine serum albumin (BSA) equivalents/g DW, respectively. In flowers cut and maintained individually, sugar and protein levels decreased rapidly after harvest, suggesting their use as respiratory substrates. Sprig senescence was characterised by loss in fresh weight and decreasing water use. In flowers taken from sprigs in vases, sugar and protein levels increased slightly (Day 4) before decre...

Carnations: effects of high concentrations of carbon dioxide on flower physiology and longevity

Abstract Elevated carbon dioxide atmosphere treatments (60% carbon dioxide in air) were applied for 1 or 3 days at 0 or 20°C to cut white carnation flowers (cv. Delphi) as a potential disinfestation treatment. Water uptake, flower diameter, respiration rate, ethylene production, longevity and pH of sap expressed from petals were measured to reveal the physiological response of the carnations to the treatments. Carbon dioxide did not affect longevity at 0 or 20°C. The higher temperature was more detrimental to the flowers than was 60% carbon dioxide. High temperature induced earlier peaks in rates of respiration and ethylene production. There was a transient yellowing of the petals upon removal from the 60% carbon dioxide treatments at 20°C. The pH of extracts from these petals was about 7 compared with pH 6 of the extracts from petals that did not yellow. We conclude carnation flowers can withstand 60% carbon dioxide at 0°C without detriment to vase life, conditions that could constitute a disinfestation treatment against some insects.

Postharvest lipid loss, malate accumulation, and appearance of malate synthase activity in asparagus spear tips

Abstract Lipid levels, glyoxylate-cycle enzymes and respiratory quotients were measured in 3 cm tips of asparagus spears (Asparagus officinalis L.) during 5 days of storage at 20°C, to determine whether lipids are mobilised as in some other senescing plant tissues. Within 12 h, the respiratory quotient dropped from near unity to 0.66 before stabilising around 0.75 after 2 days. Over 5 days of storage, almost half of the total lipid in spear tips was lost. Malate synthase (EC 4.1.3.2) activity, which was not detectable at harvest, appeared after 1–2 days and continued to increase throughout the remaining 3 days. Malate concentration increased 3- to 4-fold in 4–5 days. Isocitrate lyase (EC 4.1.3.1) activity was not detected at any time during storage, and it is unlikely that the glyoxylate cycle functions in tips of harvested asparagus spears. These results are discussed in relation to other postharvest metabolic events in asparagus.

Effect of hot water dips on botrytis storage rot and quality of kiwifruit

Abstract Hot water dips at 46, 48 and 50°C for 4, 8 or 15 min were tested for the control of botrytis storage rot in kiwifruit. Fruit were stored in air at 0°C for up to 13 weeks after the treatments. Dipping fruit at 46°C for 15 min and 48°C for 8 min gave almost complete disease control without heat injury. Fruit firmness was not affected by these treatments. Treatments which provided disease control did not affect fruit taste. Dipping at 48° for 15 min injured fruit. Injury was characterised by high rates of respiration and ethylene production, premature softening and enhanced incidence of disease.

Tiprot in asparagus: effect of temperature during spear growth

Abstract Tiprot, a postharvest disorder of asparagus, occurred at high frequency (99%) in spears grown at 20 °C in controlled temperature conditions, but at low frequency (3%) in spears grown at 13 °C. During spear growth, if temperatures of spears and crowns were controlled separately at 13 and 20 °C or at 20 and 13 °C, respectively, incidence of tiprot was similar at 56–62%. The occurrence of tiprot was negatively correlated with sucrose content of the spear tip, and positively correlated with spear tip respiration rate and spear height growth rate. Sucrose content of the spear tip at harvest gives the most practical measure of predisposition to tiprot during storage but may not be the primary cause of the disorder.

Heat production and respiration by broccoli florets during senescence at 20°C

Abstract Broccoli (Brassica oleracea L. var. italica ’ Shogun’ ) branchlets were treated with water or 50 ppm 6‐benzylaminopurine (BAP) and stored for up to 5 days in the dark at 20°C. Florets were removed from the branchlets and subjected to measurements of metabolic activity (heat production or oxygen uptake) and colour change. Water‐treated florets turned yellow much sooner than did BAP‐treated florets. Heat production and respiration decreased after both treatments, and then increased dramatically between 24 and 96 h in water‐treated florets, but increased only slightly in BAP‐treated florets. We discuss possible causes for the higher metabolic activity in water‐treated florets.

Influence of CO2 and temperature on the incidence of botrytis storage rot in beans

Abstract The effect of high levels of CO2 at 20 or 40°C for 10 or 16 h on botrytis storage rot in beans (Phaseolus vulgaris L.) was assessed. Beans were inoculated with Botrytis cinerea spores, exposed to the treatments, and stored in air for 5 days after the treatments to allow for disease expression and to assess quality. Air at 40°C for 16 h gave complete control of botrytis storage rot. High levels of CO2 (60%) were not effective and adversely affected respiration rate, firmness, and colour of the beans.