Effects of sodium alginate coating and cold plasma treatment on biochemical changes, microbial load, and microstructure of 'Granny Smith' apples during storage

Sifundo Mathe; Ngoako F. Monyela; Zinash A. Belay; Valmary M. van Breda; Oluwafemi J. Caleb; Sifundo Mathe; Ngoako F. Monyela; Zinash A. Belay; Valmary M. van Breda; Oluwafemi J. Caleb

doi:10.48130/tihort-0024-0029

Figures (5) Tables (2)

Figure 1.
Percentage weight loss of C = control; CO = sodium alginate coating; CP = cold plasma and CCP = plasma-activated coating treated 'Granny Smith' apples during storage at 15 °C for 5 weeks. Mean values (n = 9). Error bars indicate ± standard deviation of means at p ≤ 0.05. Different letters above the error bars indicate the statistically different means at p ≤ 0.05.
Figure 2.
Respiration rate of C = control; CO = sodium alginate coating; CP = cold plasma, and CCP = plasma-activated coating treated 'Granny Smith' apples during storage at 15 °C for 5 weeks. Mean values (n = 3). Error bars indicate ± SD of means at p ≤ 0.05. Different letters above the error bars indicate the statistically different means at p ≤ 0.05.
Figure 3.
(a) Total aerobic mesophilic bacteria, and (b) yeast and mold counts of 'Granny Smith' apple, C is control, CO is sodium alginate coating, CP is cold plasma treated, and CCP is sodium lignite coated and cold plasma treated samples storage at 15 °C for 5 weeks. Mean values (n = 9). Error bars indicate ± SE of means at p ≤ 0.05. Different letters above the error bars indicate the statistically different means at p ≤ 0.05.
Figure 4.
Scanning electron microscopy (SEM) images of the peel surface of apple fruit at different postharvest handling conditions. (a₁−a₃) Control (un treated), (b₁−b₃) plasma treated (CP) fruit peel, (c₁−c₃) sodium aliginate coated (CO) fruit peel, (d₁−d₃) sodium alginate coated and plasma treated fruit peel (CCP) at day zero, week 3 and week 5 of storage.
Figure 5.
Visual appearnace of 'Granny Smith' apple fruit during five weeks storage duration under different treatment conditions.

Quality parameters	Storage duration	Treatments
Quality parameters	Storage duration	Control	CO	CP	CCP
TA (g·100 mL⁻¹)	Baseline	11.13 ± 0.14^a_A
	Week-1	10.03 ± 0.04^d_B	10.44 ± 0.02^c_A	10.79 ± 0.13^b_A	11.06 ± 0.03^a_A
	Week-2	9.39 ± 0.03^f_C	9.44 ± 0.01^f_B	9.56 ± 0.07^ef_B	9.77 ± 0.06^e_B
	Week-3	8.78 ± 0.01^g_D	8.92 ± 0.04^g_C	9.01 ± 0.04^g_C	9.24 ± 0.11^fg_B
	Week-4	8.40 ± 0.04ⁱ_E	8.58 ± 0.06^hi_C	8.65 ± 0.03^h_D	8.72 ± 0.01^gh_C
	Week-5	6.84 ± 0.05^k_D	7.45 ± 0.23^j_D	7.96 ±0.15^j_E	8.24 ± 0.06^ij_C
TSS (°Brix)	Baseline	13.11 ± 0.48^a_B
	Week-1	13.00 ± 0.62^ab_C	12.70 ± 0.53^ab_B	12.70 ± 0.75^ab_B	12.70 ± 0.60^abc_B
	Week-2	13.10 ± 0.10^ab_B	12.97 ± 0.32^ab_B	12.57 ± 0.47^ab_C	12.47 ± 0.38^b_C
	Week-3	13.00 ± 0.78^a_C	12.80 ± 0.95^ab_C	12.50 ± 0.53^ab_C	12.50 ± 0.30^b_C
	Week-4	13.73 ± 0.32^a_A	13.13 ± 0.25^a_B	12.87 ± 0.31^ab_B	12.77 ± 0.70^ab_B
	Week-5	13.80 ± 0.10^a_A	13.70 ± 0.44^a_A	13.57 ± 0.49^a_A	13.43 ± 0.25^a_A
pH	Baseline	3.32 ± 0.06^a_A
	Week-1	3.20 ± 0.03^a_C	3.15 ± 0.01^a_C	3.12 ± 0.01^b_C	3.10 ± 0.01^b_C
	Week-2	3.28 ± 0.01^a_B	3.28 ± 0.01^a_B	3.27 ± 0.00^a_B	3.25 ± 0.01^a_B
	Week-3	3.31 ± 0.00^a_A	3.31 ± 0.01^a_A	3.30 ± 0.01^a_A	3.29 ± 0.00^a_A
	Week-4	3.33 ± 0.00^a_A	3.33 ± 0.00^a_A	3.32 ± 0.01^a_A	3.32 ± 0.01^a_A
	Week-5	3.46 ± 0.05^a_A	3.40 ± 0.02^a_A	3.36 ± 0.01^a_A	3.34 ± 0.00^a_A
Data presented means (n = 3) ± standard error, different lower-case letters in rows and upper case in columns represents statistically significant differences based on Duncan's Multiple Range Test at p ≤ 0.05 on TA, TSS, and pH of the fruit.

Table 1.

Effects of coating, cold plasma, and cold plasma modified coating on TA, TSS, and pH of 'Granny Smith' apples during storage at 15 °C for 5 weeks.

Quality parameters	Treatments	Storage duration (weeks)
Quality parameters	Treatments	Week-0	Week-1	Week-2	Week-3	Week-4	Week-5
L*	Control	61.6 ± 0.13^a	61.6 ± 0.51^f _A	64.8 ± 0.35^de_A	66.9 ± 1.02^cd_A	69.5 ± 1.20^bc_A	70.8 ± 1.32^ab_A
	Coated (CO)		62.5 ± 0.35^f_A	65.4 ± 0.82^d_A	66.3 ± 0.48^d_B	68.0 ± 0.36^bc_A	72.2 ± 0.17^a_A
	CP		62.3 ± 0.44^f_A	62.1 ± 1.25^f_B	61.4 ± 0.71^f_C	62.7 ± 0.20^ef_B	63.0 ± 1.82^def_B
	CCP		63.4 ± 1.31^def_A	61.9 ± 1.04^f_BC	61.5 ± 1.41^f_C	63.2 ± 0.46^ef_B	62.8 ± 0.79^f_B
a*	Control	−19.5± 0.47^a	−20.4 ± 0.58^a_A	−17.9 ± 0.19^b_C	−17.0 ± 0.06^a_B	−16.0 ± 0.77^a_C	−16.1 ± 0.33^b_B
	Coated (CO)		−19.9 ± 0.37^a_B	−18.4 ± 0.13^a_B	−18.0 ± 0.44^a_A	−16.0 ± 0.13^a_C	−14.6 ± 0.09^c_C
	CP		−20.0 ± 0.09^a_A	−19.3 ± 0.28^a_A	−18.8 ± 0.66^a_A	−19.5 ± 0.04^a_A	−18.7 ± 0.81^a_A
	CCP		−19.3 ± 0.25^a_B	−19.8 ± 0.56^a_A	−17.4 ± 0.39^b_B	−18.6 ± 0.11^a_B	−19.4 ± 0.71^a_A
b*	Control	42.4 ± 0.43^f	44.8 ± 0.22^def_A	45.8 ± 0.62^d_A	48.3 ± 0.78^bc_A	48.9 ± 0.28^b_A	50.7 ± 1.26^ab_A
	Coated (CO)		45.0 ± 0.61^de_A	46.1 ± 0.65^cd_A	47.8 ± 0.74^bc_A	49.0 ± 0.46^b_A	51.0 ± 0.27^a_A
	CP		43.8 ± 0.60^ef_B	42.7 ± 1.22^f_B	42.2 ± 0.45^f_B	43.0 ± 0.14^f_B	43.5 ± 1.84^ef_B
	CCP		43.6 ± 0.75^f_B	43.1 ± 0.15^f_B	42.8 ± 0.86^f_B	44.2 ± 0.16^e_B	44.8 ± 0.21^e_B
h°	Control	114.7 ± 0.34^a	114.5 ± 1.04^a_A	111.3 ± 1.38^bc_B	109.4 ± 1.04^cd_C	108.1 ± 0.73^d_C	107.6 ± 1.94^cd_B
	Coated (CO)		113.9 ± 1.01^a_A	111.8 ± 0.09^b_B	110.7 ± 0.19^c_C	108.1 ± 2.98^cd_C	106.0 ± 2.20^d_B
	CP		114.6 ± 0.38^a_A	114.4 ± 0.12^a_A	114.0 ± 1.31^a_A	114.4 ± 0.37^a_A	113.3 ± 1.16^ab_A
	CCP		112.7 ± 1.06^abc_A	112.3 ± 0.21^b_B	112.3 ± 0.21^b_B	112.7 ± 0.31^b_B	113.3 ± 0.15^ab_A
C*	Control	46.7 ± 0.56^a	49.3 ± 0.35^bc_A	49.2 ± 0.55^b_A	51.2 ± 0.72^a_A	51.5 ± 0.55^a_A	53.2 ± 1.07^a_A
	Coated (CO)		49.2 ± 0.53^bc_A	49.7 ± 0.65^b_A	51.1 ± 0.63^a_A	51.6 ± 0.48^a_A	53.1 ± 0.29^a_A
	CP		48.1 ± 0.59^cd_B	46.9 ± 1.00^de_C	46.2 ± 0.62^e_B	47.2 ± 0.15^d_B	47.4 ± 1.40^c_B
	CCP		47.9 ± 0.69^d_C	47.3 ± 0.31^d_B	47.0 ± 0.64^d_B	48.0 ± 0.11^c_B	48.9 ± 0.27^bc_B
Firmness (N)	Control	7.00 ± 0.01^a	6.82 ± 0.00^b_D	6.59 ± 0.02^c_D	6.26 ± 0.02^e_D	5.19 ± 0.07^fg_D	4.33 ± 0.15^h_D
	Coated (CO)		6.87 ± 0.04^b_C	6.63 ± 0.01^c_C	6.32 ± 0.04^d_C	5.64 ± 0.10^f_C	4.54 ± 0.36^g_C
	CP		6.94 ± 0.01^a_B	6.69 ± 0.00^b_B	6.41 ± 0.01^d_B	5.95 ± 0.06^ef_B	4.67 ± 0.78^f_B
	CCP		6.98 ± 0.01^a_A	6.78 ± 0.03^a_A	6.48 ± 0.03^cd_A	6.11 ± 0.08^e_A	5.16 ± 0.18^g_A
Data presented are means (n = 12) ± standard error, different lower-case letters in rows and upper case in columns represents statistically significant differences based on Duncan's Multiple Range Test at p ≤ 0.05 on peel colour of the fruit. CP = cold plasma treated.

Table 2.

Effect of different treatments on color attributes and firmness of cv. 'Granny Smith' apple coated with sodium alginate treated with cold plasma and stored at 15 °C and 90% ± 2% RH for 5 weeks.