Elsevier

Food Chemistry

Volume 61, Issue 3, 31 March 1998, Pages 293-300
Food Chemistry

Chemical compounds and sensory assessment of kiwifruit (Actinidia chinensis (Planch.) var. chinensis): electrochemical and multivariate analyses

https://doi.org/10.1016/S0308-8146(97)00052-6Get rights and content

Abstract

This study reports the analytical and sensory analyses made on selected kiwifruit genotypes (Actinidia chinensis (Planch.) var. chinensis) produced from seeds of fruit gathered in the Guangxi region of the People’s Republic of China. The analytical measurements of some soluble sugars, such as glucose and fructose, and non-volatile acids, such as malic and ascorbic acid, were carried out using innovative analytical procedures based on fast and selective devices that require very little or no sample treatment. The multivariate techniques, Principal Component Analysis and Cluster Analysis, useful when many variables are involved, allowed the classification of kiwifruit genotypes according to sugar and non-volatile acid contents and sensory properties. Citric acid, the major organic acid, ranged from 0.8 to 1.8 g per 100 g of fresh weight and malic acid content was 0.1–0.5 g per 100 g of fresh weight. The levels of fructose and glucose (present in approximately equal amounts in most of the genotypes analysed), were higher than that of sucrose in almost all the genotypes. Ascorbic acid content in kiwifruit samples from genotypes of Actinidia chinensis (Planch.) var. chinensis was higher than the typical mean content in Actinidia chinensis var. deliciosa (A Chev) cv Hayward. Sensory assessment showed that total fruit aroma and flavour were the best discriminating attributes and were highly correlated with overall quality. No consistent correlation was found between overall quality and the sensory attributes of sweetness, juiciness and firmness.

Introduction

The most widely grown kiwifruit crop is the Actinidia chinensis var. deliciosa (A Chev) cv Hayward. The commercial growing of this variety has spread to many countries because of its distinctive characteristics, such as size, uniformity of speckling and postharvest quality. Several investigations were carried out on changes in composition and the softening of Actinidia chinensis var. deliciosa cv Hayward during ripening (Mac Rae et al., 1989) and postharvest treatments. Stec et al. (1989) found that parameters such as aroma intensity and acceptability, sweetness, acidity and ripe fruit flavour were significantly affected by the firmness of the fruit.

Kiwifruit contains significant amounts of vitamin C (l-ascorbic and l-dehydroascorbic acids) which is physiologically active in both forms (Wills & Greenfield, 1981). It contains more than the average amounts found in fruit such as grapefruit, oranges, strawberries and lemons and ten times as much as that found in apples and peaches (Beever & Hopkirk, 1990).

Inconsistencies in reported values for kiwifruit are largely owing to differences in varieties, degree of maturity, storage and method of analysis. For instance, the value range for ‘Hayward’ fruit was 37–200 mg per 100 g of fresh weight (Selman, 1983, Lintas et al., 1991). However, very little is known about the chemical composition, particularly ascorbic acid content and the sensory evaluation of other kiwifruit genotypes.

The objective of this work was to carry out analytical and sensory analyses in order to characterise selected genotypes of Actinidia chinensis (Planch.) var. chinensis originating from seeds of fruit gathered in the Guangxi region of the People’s Republic of China that could contribute to improving the world’s varieties.

The analytical measurements of ascorbic acid and certain soluble sugars and non-volatile acids were carried out using innovative analytical procedures based on fast and selective devices which require very little or no sample treatment (Mascini & Palleschi, 1989). In addition, the use of glucose, fructose, malic and ascorbic acid probes for the genetic improvement of the fruit produced good results.

Section snippets

Kiwifruit

Twenty-three early-maturing (35–24 days before cv Hayward) kiwi genotypes (Actinidia chinensis (Planch.) var. chinensis) (Table 1) were obtained from the experimental orchards of the Istituto Sperimentale per la Frutticoltura (Fiorano, Rome, Italy). The trees were about 7 years old, grafted on the same rootstock, spaced at 4×2.5 m and trained on multi-wired fences. The fruit skin of some genotypes is thin and covered with very fine hairs that are largely deciduous, whereas others are completely

Analytical optimisation

Calibration curves of glucose, malate, fructose and ascorbate, carried out with electrochemical biosensors, led to the results reported in Table 2, which shows the lower and upper detection limits, the linearity range and the relative standard deviation calculated on three consecutive measurements at a fixed standard concentration and with selected samples of fruit. The probes gave good reproducible results. Calibrations were performed during fruit analysis and both stability and drift probes

Conclusion

The multivariate techniques of analysis applied have been useful for classifying the kiwifruit genotypes into two groups: low and high non-volatile acid content. The sensory analysis was useful as it introduced further information other than soluble sugar and non-volatile acid content. Moreover, the overall quality of the kiwifruit genotypes depends more on the aroma of the fruit than on taste (sweet, sour) or mouthfeel.

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