Fruit source and storage procedure
Persimmon fruits cv. “Rojo Brillante” were harvested in LAlcudia (Valencia) and transported to Technidex S.A Co. (Valencia, Spain), where fruits were carefully selected for uniformity of size and color development. Afterward, the fruits were separated in lots according to the following controlled atmosphere (CA) treatments in triplicate: air or control (CTL), 10% CO2+ 90% N2 (CA1), and 97% N2+ air (CA2). The fruits were always maintained at 15 °C with 85% to 90% R.H. After 20-, 30-, 40-, and 50-d storage, a sample of fruit from each replicate was transported to Inst. Valenciano de Investigaciones Agrarias (IVIA), and submitted to deastringency treatment. Subsequently, the fruits were transferred to 20 °C in air free of CO2 for 5 d to simulate shelf life period.
Deastringency treatment was carried out in closed containers that contained 95% CO2 for 24 h at 20 °C (90% R.H.) by passing a stream of air containing 95% CO2 through the containers.
Other samples of CA-treatments were transferred directly from 15 °C to shelf life conditions, without being submitted previously to deastringency treatment. These treatments were named “direct commercialization” (DC) treatments (DC-CA1 and DC-CA2).
Fruit quality assessment
After storage periods at 15 °C and after subsequent shelf life, flesh firmness, astringency, acetaldehyde, ethanol, total soluble solids, pH, external color, respiration rate, ethylene production, sensory evaluation, and external and internal disorders were evaluated.
Flesh firmness was determined over 20 fruits per replicate, with a Texturometer Instron Universal Machine model 4301 (Instron Corp., Canton, Mass., U.S.A.), using an 8-mm plunger, after epicarp removal, at 2 equidistant locations in the equatorial region of each fruit. The crosshead speed during the firmness testing was 10 mm/min. Data were expressed as the maximum force in Newtons (N) required to break the flesh.
Astringency level of fruit was estimated by soluble tannins (ST) analysis, tannin content index (TI) determination, and sensory evaluation.
Many of 15 fruits per replicate were divided in 3 samples and cut in four longitudinal parts. Two of the opposite parts were sliced and frozen (–20 °C) to determine ST, which was evaluated using the Folin–Denis method as described by Arnal and Del Rio (2004b) and expressed as percentage or g/100 g F.W.
To determine TI (Gorini and Testoni 1988), 5 fruits were visually evaluated from each replicate. Soluble tannins, which are responsible for persimmon astringency, are compounds that react with ferric chloride, forming tannin–Fe ion complexes, which are blue–black. The degree of astringency can be estimated in persimmon fruit by evaluating color development during the reaction. Persimmon fruits were cut equatorially and after 15 min the freshly cut surface was immersed in a 5% FeCl3 solution for 3 min. After another 3 min out of the solution, the color of freshly cut surface was visually evaluated from 1 (less color development or minimum tannin content, no astringency) to 5 (maximum color development or maximum tannin content, high astringency).
Sensory evaluation was performed at the sensory Laboratory of the Postharvest Dept. of the IVIA in composite samples of 5 fruits from each replicate previously peeled and sliced. Eight to 10 semitrained judges were asked to evaluate astringency and the presence of off-flavors. The judges were persons familiar with cultivar “Rojo Brillante” who were tasting fruits with different levels of astringency for several years. A 4-point scale was used for astringency, where 1 = very high astringency and 4 = no astringency. Each sample consisted of segments taken from about 5 individual fruits. Samples were presented to panelists in trays labeled with 3-digit random codes and served at room temperature (25 ± 1 °C). The panelists had to taste several segments of each sample in order to compensate, as far as possible, for biological variation of the material. Milk was provided for palate rinsing between samples.
The opposite parts of the fruit, which were not used to measure astringency, were placed in an electric juice extractor (model 753, Moulinex, Spain) and filtered through cheesecloth; obtained juice was used to determine acetaldehyde and ethanol production, total soluble solids (TSS), and pH.
Acetaldehyde and ethanol production were measured on 3 samples per replicate of juice samples, obtained as mentioned previously and analyzed by headspace gas chromatography (Ke and Kader 1990). Five milliliters of the filtered juice were transferred to 10 mL vials with crimp-top caps, sealed with TFE/silicone septa, and frozen (–20 °C) until analysis. For the analysis, the samples were put in a water bath at 20 °C for 1 h, followed by heating at 60 °C for 10 min. A 1-mL sample of the headspace was withdrawn from the vials and injected in the gas chromatograph (Perkin-Elmer, Model 2000, Norwalk, Conn., U.S.A.), provided with flame ionization detector (FID) and 0.32 cm × 1.2 m Poropak QS 80/100 column. The injector was set at 175 °C, the column at 150 °C, the detector at 200 °C, and the carrier gas at 12.3 psi. Ethanol and acetaldehyde were identified by comparison of retention times with those of a standard solution. The results were expressed as mg/100 mL.
TSS were measured twice from 3 juice sample per replicate with a digital refractometer (model PR1, Atago, Tokyo, Japan) and the results were expressed as °Brix. Measures of pH were done with a pH-meter (model C231, Consort, Belgium).
Skin color was evaluated by a Minolta Colorimeter (Model CR-300, Ramsey, N.Y., U.S.A) on samples of 20 fruit. L, a, b Hunter parameters were measured, and the results were expressed as skin color index as described by Jiménez-Cuesta and others (1981); color index = (1000a)/(Lb).
Ethylene and carbon dioxide production rates were measured in 3 replicates of 2 fruits per replicate. The fruits were weighed and sealed in 2-L glass jars for 2 h at 20 °C. Ethylene and carbon dioxide were analyzed by injecting 3 samples per replicate of 1 mL of headspace into a gas chromatograph (Perkin Elmer), as described by Salvador and others (2005). CO2 production was expressed as mL CO2/kg/h and ethylene production as μLC2H4/kg/h.
External or internal browning was visually assessed as slight (<25% of the affected area), medium (25% to 50% of the affected area), or severe (>50% of the affected area), in samples of 50 fruits per replicate.