Peel firmness

4. IN VITRO AND IN VIVO DISINFECTION AND BIOCONTROL TREATMENTS

5.6 Results and Discussion

5.6.4 Peel firmness

Table 5.7 presents the change in firmness of P. digitatum-inoculated kumquat fruit subjected to different pre-packaging treatments over a 28-day storage period. The treatments did not have a significant (P0.05) influence on the peel firmness. A general decrease in the peel firmness can be observed from Day 0 to Day 28. However, a localized increase in firmness occurred, particularly in the control samples. A substantial increase in the firmness was observed between Days 14 (7.30 N) and 28 (9.04 N). Kumquats

treated with chlorinated water only displayed the least firmness (7.05 N), which is concomitant with the greatest PWL (86.17%) and lowest moisture content (40.53%), as indicated in Tables 5.2 and 5.9, respectively. Chlorinated water + B13 also displayed low fruit firmness on Day 28 of 7.10 N.

Table 5.7 Changes in the peel firmness (N) 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 11.71^e 6.99^a 6.10^a 6.99^a 7.05^a Anolyte water 11.71^e 10.60^de 8.08^ab 7.05^a 7.56^ab

Hot water 11.71^e 7.82^ab 7.57^ab 7.04^a 7.90^ab

Biocontrol (B13) 11.71^e 7.38^ab 7.41^ab 8.30^ab 8.48^ab Chlorinated water + HWT 11.71^e 7.63^ab 7.98^ab 7.84^ab 7.20^a Chlorinated water + B13 11.71^e 7.66^ab 7.90^ab 7.06^a 7.10^a Chlorinated water + HWT + B13 11.71^e 7.36^ab 7.84^ab 7.54^ab 7.57^ab Anolyte water + HWT 11.71^e 8.16^ab 9.07^cde 7.83^ab 7.68^ab Anolyte water + B13 11.71^e 7.98^ab 8.90^cde 5.86^a 7.57^ab Anolyte water + HWT + B13 11.71^e 8.71^abc 7.98^ab 8.51^ab 7.85^ab

HWT + B13 11.71^e 7.34^ab 7.88^ab 7.55^ab 7.82^ab

Control 11.71^e 8.12^ab 7.30^a 8.75^bcd 9.04^cde

Significance

Treatment (A) NS

Storage Period (B) **

AB NS

CV (%) 18.5

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’.

Table 5.8 shows the variation in the firmness of kumquat fruit inoculated with P. italicum and subjected to different pre-packaging treatments. Unlike with P. digitatum-inoculated fruit, the treatment and storage period had a highly significant (P≤0.001) influence on the peel firmness. The control fruit exhibited the greatest increase in the firmness from Day 0 to Day 28 from 7.24 N to 12.76 N, amounting to a 76% increase in the firmness. The integration of chlorinated water and B13 also resulted in a large increase in the firmness

from Day 0 to Day 28 of 52%. This could largely be attributed to a reduction in the moisture content giving rise to a hard and leathery peel (Ladaniya, 2008).

Table 5.8 Changes in the peel firmness (N) 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 7.24^ab 7.47^abc 8.59^cd 9.18^de 9.36^def

Anolyte water 7.24^ab 7.04^a 7.25^ab 8.17^bcd 10.34^gh

Hot water 7.24^ab 7.17^a 7.18^a 7.38^ab 9.69^efg

Biocontrol (B13) 7.24^ab 7.65^abc 7.80^bc 8.31^cd 10.72^hi Chlorinated water + HWT 7.24^ab 7.14^a 7.53^abc 7.83^bc 8.42^cd Chlorinated water + B13 7.24^ab 7.67^abc 7.39^ab 8.66^cd 10.97^j Chlorinated water + HWT + B13 7.24^ab 8.03^bcd 7.48^abc 8.46^cd 8.39^cd Anolyte water + HWT 7.24^ab 7.86^bc 8.02^bcd 9.45^ef 9.96^fg Anolyte water + B13 7.24^ab 8.15^bcd 8.21^bcd 8.56^cd 8.93^cd Anolyte water + HWT + B13 7.24^ab 7.04^a 6.96^a 7.81^bc 8.02^bcd

HWT + B13 7.24^ab 7.64^abc 7.73^bc 8.48^cd 8.62^cd

Control 7.24^ab 7.41^ab 9.18^de 10.79^hi 12.76^k

Significance

Treatment (A) **

Storage Period (B) **

AB **

CV (%) 10.3

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’.

The combined effect of anolyte water, hot water and B13 maintained the fruit firmness, which was evident in only an 11% increase in the fruit firmness. Chlorinated water combined with hot water and B13 as well as chlorinated water combined with hot water also demonstrated minimal variation in the fruit firmness of 16% throughout the storage period. Control fruit exhibited an increase in peel firmness associated with tissue lignification.

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.