Fresh-cut Red Delicious apples coating using tocopherol/mucilage nanoemulsion: Effect of coating on polyphenol oxidase and pectin methylesterase activities

Abstract

The objective of this research was to determine the effect of α-tocopherol emulsion coatings with different particle sizes, with and without nopal mucilage (Opuntia ficus indica), applied to fresh-cut apples to evaluate pectin methylesterase (PME) and polyphenol oxidase (PPO) activity and changes associated with texture and the browning index at 4°C for 21days. The systems were: emulsion/mucilage; nanoemulsion; nanoemulsion/mucilage and solution all these with 2g/L α-tocopherol; mucilage; and untreated apples. All treatments were applied by immersion. The particle size of the emulsions was 1281nm with a zeta potential of −35mV, while the nanoemulsions were <200nm with a zeta potential of <−40mV, indicating stable systems. Respiration rate decreased to 35 mL O2/kg h when the apple was coated with nanoemulsions, compared to the control, α-tocopherol solution and mucilage (73, 63 and 61mL O2/kgh). PME activity in the coated apples was lower in the submicron-size samples, helping maintain the firmness of the apples coated with nanoemulsion/mucilage (6.2N) and nanoemulsion (5.1N), compared to controls (2.7N). At 21days of storage, PPO activity decreased by 65% in the apples with nanoemulsion, as reflected in the lower browning indexes of 43.5 for nanoemulsions and 39.3 for nanoemulsion/mucilage. We conclude that the particle size of the emulsion droplets is a determining parameter in controlling texture and the browning index. The use of nopal mucilage helps control the browning index and is thus an additive with high potential for use in the preparation of nanocoatings.