Firmness is one of the important parameters reflecting thepostharvest storage characteristic of fruits. It is related to tissuesoftening. Loss of firmness caused by the loss of integrity of cellwallstructure leads to wilting and shrinking of fruits (Qi et al., 2011). Asshown in Fig. 1b, firmness of the initial samples was 3.19 N beforeany treatments. After 1 day of coating processing, firmness of calciumtreated groups was significantly (P < 0.05) higher than untreatedcontrol group. With calcium salt treatment, the firmness offruit increased slightly in the first couple of days of storage; thismight be due to chelate effect of calcium ions on pectin and otherrelated macromolecules within fruit flesh, leading to increasedfirmness. This finding is consistent with previous reports(Ngamchuachit, Sivertsen, Mitcham, & Barrett, 2014; Saftner, Bai,Abbott, & Lee, 2003; Varela, Salvador, & Fiszman, 2007). The concentrationof coating solution was very low (<3%) in all the groups.After treatment and drying, the coating layer was very thin, thusthe firmness determined can be viewed as fruit itself thoughtheoretically it might be partially contributed by the coating layer.This contribution to firmness by coating layer was not counted byprevious reports of similar research as well (Ngamchuachit et al.,2014; Saftner et al., 2003; Varela et al., 2007). During day 1 today 13, storage, firmness of all samples decreased. In addition, therates of tissue softening were significantly different (P < 0.05) betweencontrol and all treated group. The highest firmness wasobserved in combined chitosan and calcium chloride treated samples,of which the firmness was within the range of 4.26 Ne3.70 Nin 13 days of storage, followed by calcium only treated samples andchitosan only coated samples. The current results were in agreementwith previous reports that chitosan coating and calciumdipping are effective in preserving the firmness of fruits(Hernandez-Munoz et al., 2008; Liu et al., 2009; Qi et al., 2011; Xiaoet al., 2010).
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