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  • Author or Editor: Nicky G. Seager x
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Experiments investigating kiwifruit [Actinidia deliciosa (A. Chev) C.F. Liang et A.R. Ferguson var. deliciosa] maturation were undertaken requiring the determination of total soluble sugar (TSS) and starch concentrations in numerous fruit samples. The phenol-sulfuric acid assay was judged to he a convenient method for determining TSS from tissue extracts and gave results similar to those obtained by high-pressure liquid chromatography. The starch procedure adopted involved gelatinizing fruit tissue using hot water and a thermostable α -amylase (Termamyl); hydrolizing starch using amyloglucosidase; and determining glucose using glucose oxidase. The methods enabled one person to analyze up to 40 kiwifruit samples for TSS and starch concentrations during 9 hours and likely will be applicable to research concerning fruit development and maturation.

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In New Zealand, harvest maturity for kiwifruit is determined by the soluble solids concentration (SSC) of juice (minimum 6.2%). Commercial maturity differs in various regions of the country within each season and between years and may be due to differences in temperatures during growth.

Mature `Hayward' kiwifruit vines were grown in controlled environment temperature treatments of 14/8, 18/8, 22/8, 26/8, 14/12 and 22/12C to determine whether the increase in SSC at low night temperatures recorded in a related study was a result of the mean temperature, the min. daily temperature, or the magnitude of the max./min. temperature difference. Measurement was made of fruit size, firmness, starch and total sugar concentrations in the fruit at 10 day intervals.

SSC increased fastest with the coolest mean temperature irrespective of the min. temperature or max./min. difference. In the coolest treatment the concentration of starch decreased rapidly with a rise in total sugar, in the warmest treatment the change in the carbohydrate components was slower. Data will be used to predict harvest date at commercial orchard sites based on field temperature measurements.

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