Firmness

A Fruit Texture Analyzer (FTA 20, Güss, South Africa) with 11.1 mm compression probe was used to measure flesh firmness [28]. To measure flesh firmness for each replicate (10 fruit), each fruit was peeled equatorially on opposite sides, the plunger was pressed into the peeled flesh, and the firmness reading recorded. The operating conditions of the instrument were: pre-test speed 1.5 mm s<sup>−</sup>1, 0.5 mm s−<sup>1</sup> test speed, 10.0 mm s−<sup>1</sup> post-test speed, and 0.20 N trigger force. The average reading from both sides was used.

#### Total Soluble Solids and Titratable Acidity

To measure total soluble solids (TSS), fruit segments (≈20 g of each fruit) were cut transversely from 10 randomly selected fruit per replicate. The fruit segments were processed for juice using a domestic juicer (Mellerware Liquafresh juice extractor III). The juice was homogenized by mixing and stabilizing for five minutes, and 5 mL was sampled using a syringe for TSS measurements. Total soluble solids content was obtained using a calibrated refractometer (Pocket refractometer PAL<sup>−</sup>1, ATAGO Co. LTD, Tokyo, Japan) [29]. Standardization was done using distilled water (refractive index of 0). The refractometer was rinsed between readings to maintain accurate measurements of TSS. To measure titratable acidity (TA), 20 g of fruit segments were cut from each of the 10 fruit (per replicate) and a 46 mL juice sample was blended and titrated against 0.333 N of sodium hydroxide (NaOH) to a pH of 8.2 using a Crison Titromatic 1S/2B (Crison Instruments, Barcelona, Spain). Titratable acidity was expressed as g of malic acid per 100 g [29].

#### Background Color

A Chroma Meter (CR 400/410 Konica Minolta Sensing Inc., Japan) was used to obtain background color according to the Commission Internationale De I'Eclairage (CIELAB)(L\*, a\* and b\*) system from two opposite positions along the equatorial region of the fruit [30]. The color coordinate L\* = 0 to 100 (describing black to white), a\* = red (+)/green (−), and b\* = yellow (+)/blue (−). Hue angle (h◦) was used to measure background color and determined according to the following Equation (1):

$$\mathbf{h}^{\circ} = \arctan \left( \mathbf{b}^{\star} / \mathbf{a}^{\star} \right) \tag{1}$$

where a\* represents redness and greenness and b\* represents yellowness and blueness.

#### 2.2.3. Headspace Volatile Analysis

Fruit were sampled at harvest, after each storage period, and after a 6 w simulated shipping and handling period followed by 7 d shelf life. Apple peel was carefully obtained from four regions of each fruit using a stainless steel peeler (Sigma–Aldrich, Johannesburg, South Africa). A sample of 10 fruit was obtained from each replicate, peeled, cut into smaller pieces, and 5 g was weighed into 20 mL solid phase microextraction (SMPE) glass vials. Ten microlitres of 3-octanol or anisole/methyoxybenzene solution were added as an internal standard to the vials, after which they were sealed. Three replicates were prepared for each treatment (1 glass vials = 1 replicate = 5 g apple peel). The solid phase microextraction (SPME) method was used for headspace volatile analysis [9,31]. Equilibration of vials was done for 10 min in an autosampler incubator (CTC Analytics AG, Zwingen, Switzerland) set at 50 ◦C. Volatile compounds in the headspace were trapped on a 50/30 μm divinylbenzene-

carboxen-polydimethylsiloxane coated fiber after exposure for 20 min at 50 ◦C. Volatile compounds on the fiber coating were then desorbed for 2 min in the injection port of the gas chromatograph, operated in splitless mode at a temperature of 250 ◦C. Preconditioning of the fiber was done for 2 min at a temperature of 50 ◦C and 250 rpm followed by volatile compound chromatographic separation using a polar capillary column (60 m 0.25 mm i.d., 0.5 μm film thickness) (Agilent Technologies DB-FFAP, model J&W 122–3263). The oven was set at a temperature of 40 ◦C, held for 5 min, and then rapidly increased to 230 ◦C for 6 min. The total run time for the method was 30 min. Helium was used as a carrier gas at a constant flow rate of 1 mL/min. The ion source and quadropole were kept at 240 ◦C and 150 ◦C, respectively. The transfer line temperature was kept at 280 ◦C.
