Peel moisture content

4. IN VITRO AND IN VIVO DISINFECTION AND BIOCONTROL TREATMENTS

5.6 Results and Discussion

5.6.5 Peel moisture content

The one-way and two-way interaction between the treatment and storage period were highly significant (P≤0.001) on the firmness of kumquat fruit. The firmness in citrus fruit depends primarily on the turgidity and weight loss (Olmo et al., 2000; Hong et al., 2007).

Olmo et al. (2000) found that a decrease in the firmness coincided with an increase in the weight loss. Studies by Rodov et al. (2000), Singh and Reddy (2006) and Hong et al.

(2007) observed a decrease in the firmness of citrus fruit during storage. This was synonymous with a decrease in the moisture content resulting in a drying effect and softening of the peel tissue. However, Ladaniya (2008) observed that with increasing moisture loss, the peel of citrus fruit becomes tough and leathery, resulting in a higher puncture resistance. This could account for the increase in firmness, particularly between Days 21 and 28 in control fruit of P. digitatum- (9.04 N) and P. italicum-inoculated control fruit (12.76 N). The postharvest storage of fruit is associated in a loss in the cell wall integrity as a result of the breakdown of pectic substances (Valero et al., 1998). This in turn leads to an increase in the soluble pectin and a decrease in the fruit firmness. The combined treatment of a biocontrol agent (Bacillus amyloliquefaciens HF-01), hot water (45°C for 120 seconds) and sodium bicarbonate (1% or 2%) resulted in firmer mandarin fruit (Hong et al., 2014).

Many studies have found the combination of hot water and chlorinated water to be effective in extending the shelf life of citrus fruit (Korf et al., 2001; Sen et al., 2007).

However, the addition of a biocontrol further improves the efficacy (Korf et al., 2001;

Sen et al., 2007). This study found that the use of anolyte water as a disinfectant in integrated treatments was more beneficial in maintaining the fruit firmness than chlorinated water. Based on the results it can be recommended that the combined use of anolyte water, hot water and B13 biocontrol be used for the maintenance of the postharvest firmness of kumquat fruit.

Table 5.9 Changes in the peel moisture content (%) of Penicillium digitatum- inoculated kumquat fruit over a 28-day storage period subjected to different integrated pre-packaging treatments

Treatment Storage Period (Days)

0 7 14 21 28

Chlorinated water 82.80^k 71.9^gh 64.2^de 56.9^bc 40.53^a Anolyte water 82.80^k 74.0^hij 63.6^cde 60.0^cd 50.1^abc

Hot water 82.80^k 66.0^ef 66.8^ef 59.1^bcd 50.1^abc

Biocontrol (B13) 82.80^k 72.6^hi 60.7^cd 59.5^cd 48.0^ab Chlorinated water + HWT 82.80^k 70.3^g 67.7^efg 59.1^bcd 58.8^bcd Chlorinated water + B13 82.80^k 75.0^hij 66.8^ef 58.2^bcd 50.3^abc Chlorinated water + HWT + B13 82.80^k 68.5^fg 67.1^ef 61.2^cde 51.1^abc Anolyte water + HWT 82.80^k 74.8^hij 64.6^de 63.9^cde 56.6^bc Anolyte water + B13 82.80^k 70.4^g 63.1^cde 58.4^bcd 52.6^abc Anolyte water + HWT + B13 82.80^k 66.0^ef 67.0^ef 62.9^cde 57.0^bcd

HWT + B13 82.80^k 71.2^gh 65.1^def 60.9^cd 51.7^abc

Control 82.80^k 68.3^fg 64.0^de 56.0^bc 42.37^a

Significance

Treatment (A) **

Storage Period (B) **

AB **

CV (%) 5.3

NS, *, ** Non-significant or significant at P≤0.05 or P≤0.001, respectively. Means within a column followed by the same letter(s) are not significantly different from each other according to Duncan’s Multiple Range Test (P≤0.05), (n=3). CV, Coefficient of variation; HWT, hot water treatment; +,

‘combined with’.

A general decrease in the MC content was observed for all treatments from Day 0 to Day 28. The greatest decline in the MC was observed in control samples and samples treated with chlorinated water only of 49% and 51% from day 0 to day 28, respectively. The least decrease in the MC was observed in fruit treated with a combination of anolyte, hot water and biocontrol (31%) and chlorinated and hot water (29%) from Day 0 to Day 28. The two-way interaction between the treatment and the storage period was also found to be highly significant (P≤0.001) with regard to the peel moisture content. The rate at which the moisture content decreased was greater toward the end of the storage period, between Days 21 and 28. This was most pronounced after individual treatments, compared to integrated treatments. Treatments that combined anolyte water as the disinfectant had

Table 5.10 represents the moisture content (MC) of the kumquat peel over a 28-day storage period that had been inoculated with P. italicum. The treatment and storage was found to significantly (P≤0.001) influence the MC. A gradual decrease in the moisture content was observed in all treatments throughout the storage period. The individual treatments resulted in kumquat fruit with lower MC than those subjected to integrated treatments. The combined treatments of (1) chlorinated water and hot water, (2) anolyte water, hot water and B13 and (2) hot water alone produced the highest MC of 56.3%, 54.6% and 54.6%, respectively, on Day 28. The individual treatments resulted in the lowest MCs on Day 28, compared to combined treatments. The two-way interaction between the treatments and storage periods was highly significant (P≤0.001) in terms of the peel moisture content. The greatest reduction in the MC was observed at the end of the storage period between days 21 and 28.

Citrus fruit have a high moisture content in both the pulp and peel (Chien et al., 2007;

Ghanema et al., 2012). Once harvested the fruit loses excessive moisture from the peel via transpiration and respiration, promoting the onset of decay caused by pathogens, thereby reducing the shelf life (Purvis, 1983). Treatments incorporating anolyte water as the disinfectant were more effective in maintain the fruit MC.

Table 5.10 Changes in the peel moisture content (%) of Penicillium italicum- inoculated kumquat fruit over a 28-day storage period subjected to different integrated pre-packaging treatments

Treatment Storage Period (Days)

0 7 14 21 28

Chlorinated water 80.4^f 70.2^cd 63.5^bc 53.1^ab 46.5^a

Anolyte water 80.4^f 70.8^cde 66.6^bcd 56.8^abc 40.0^a

Hot water 80.4^f 74.7^ef 69.0^cd 61.3^bc 54.6^ab

Biocontrol (B13) 80.4^f 70.3^cd 64.4^bc 57.1^abc 43.7^a

Chlorinated water + HWT 80.4^f 73.4^def 68.7^cd 64.6^bc 56.3^abc Chlorinated water + B13 80.4^f 71.8^de 67.5^bcd 61.2^bc 46.4^a Chlorinated water + HWT + B13 80.4^f 71.0^cde 68.9^cd 58.3^abc 50.5^ab Anolyte water + HWT 80.4^f 72.4^de 62.8^bc 62.7^bc 53.0^ab Anolyte water + B13 80.4^f 70.9^cde 65.7^bcd 56.3^abc 44.9^a Anolyte water + HWT + B13 80.4^f 72.3^de 68.9^cd 63.3^bc 54.6^ab

HWT + B13 80.4^f 70.5^cde 67.0^bcd 67.3^bcd 52.2^ab

Control 80.4^f 71.7^de 67.1^bcd 57.8^abc 50.8^ab

Significance

Treatment (A) **

Storage Period (B) **

AB **

CV (%) 5.4

NS, *, ** Non-significant or significant at P≤0.05 or P≤0.001, respectively. Means within a column followed by the same letter(s) are not significantly different from each other according to Duncan’s Multiple Range Test (P≤0.05), (n=3). CV, Coefficient of variation; HWT, hot water treatment; +, ‘combined with’.