Postharvest fruit density as an indicator of dry matter and ripened soluble solids of kiwifruit

Abstract

The density of unripe kiwifruit (Actinidia deliciosa (A. Chev.) C.F. Liang et A.R. Ferguson cv. Hayward) early in storage was investigated as a means of determining the current fruit dry matter (DM) and total sugar-plus-starch concentrations, and of predicting DM and soluble solid concentrations later when the fruit had ripened. To investigate the robustness of the density relationships with DM and ripe fruit soluble solids, measurements were made on fruit collected in a survey involving 208 New Zealand orchards ( 10% of the total) across the normal harvest season (early May-early June). Density measured on unripe fruit early in storage correlated with both DM measured at the same time (r 2 =82.6%; S.E.=0.68% fresh weight (FW)), and with SSC measured after ripening (r 2 = 85.1%; S.E. =0.57% FW). As fruit taste is related to sugar concentration, and sugars make up the bulk of the soluble solids in fruit, this suggests potential for automated bulk taste sorting of kiwifruit at harvest by floating off low DM fruit in prepared salt solutions. To investigate the reasons for the relationship between density and other fruit measurements, fruit composition was analysed. Fruit taken from storage 2 weeks after harvest were graded non-destructively by density into four distinct dry matter groups, each containing eight fruit (four pairs matched by density). Paired fruit were separated and analysed for DM, soluble solids, starch and sugars (sucrose, glucose and fructose), one fruit immediately and the other after ripening. Equations relating density to both DM and ripe fruit soluble solids in the composition trial had similar parameter values to those of the survey trial and gave S.E. of prediction of about 0.3% FW. DM levels were about 3.2% FW above the sum of soluble solids and starch concentrations in both ripe and unripe fruit, a difference largely independent of DM concentration. Starch lost during ripening was accounted for by the increase in the glucose and fructose sugar pools, and these two sugars had near equal concentrations at each DM level. Sucrose and minor sugar levels were independent of DM and ripeness.

New quality index based on dry matter and acidity proposed for Hayward kiwifruit

“…This effect of ripe titratable acidity may be explained by the fact that high dry matter is associated with sweetness (Burdon et al 2004;Jordan et al 2000), which may balance a sourness perception, as reported in kiwifruit and mango (Harker et al 2009;Malundo et al 2001). When fruit is perceived to be less sour (ripe titratable acidity < 1.2%), consumers are less demanding for high soluble sugars, or dry matter content, and they "like" kiwifruit with dry matter greater than or equal to 15.1%.…”

“…The sweetness, eating quality, consumer acceptance and repeat purchases of kiwifruit are strongly associated with the concentration of soluble sugars (Burdon et al 2004;Crisosto and Crisosto 2001;Harker et al 2009;Jordan et al 2000;Rossiter et al 2000). Following an in-store consumer test, UC researchers proposed a soluble solids concentration after ripening (RSSC) of 12.5% as the minimum quality index for early-marketed California kiwifruit (Crisosto and Crisosto 2001).…”

“…Dry matter readings include starch and are highly correlated with ripe soluble solids concentration (Beever and Hopkirk 1990;Harker et al 2009;Jordan et al 2000), and they do not change during cold storage (Crisosto et al 2009). New Zealand and Chile have started using a minimum dry matter standard for retail marketing and wholesale trade.…”

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“…Dry matter (DM) in kiwifruit (Actinidia deliciosa) has been proposed as being both a maturity indicator for the proper time of harvest and also as a predictor of the sensory quality of the fruit once ripe [3][4][5] . It comprises both the soluble solids (largely fructose, glucose, and sucrose) and insoluble solids (mainly the structural carbohydrates and starch).…”

Hydro-sorting of apricots based on some physical characteristics

“…Density, is a good indicator of fruit dry matter (Richardson et al 1997;Jordan et al 2000), thus becomes an interesting tool for the fruit quality sorting because of its inherently lower cost and simpler operation. The sorting of products based on density is not new, patents and publications, in the potato industry for example, extend from 1950s to the present day (Kunkel et al 1952;Wilson & Lindsay 1969;Bajema 2001).…”