Combined Application of Antibrowning,Heat Treatment and Modified‐Atmosphere Packaging to Extend the Shelf Life of Fresh‐Cut Lotus Root

This work aimed to determine the effects of different concentrations of antibrowning treatments (that is, distilled water [DW], 1% ascorbic acid [AA], 0.5% chamomile [CM], and 1% AA + 0.5% CM) and heat‐treatment (55 °C for 45 s) combined with packaging under 4 different modified‐atmosphere gas compositions (that is, air, vacuum, 100% CO₂, 50% CO₂/50% N₂) on the quality and microbiological characteristics of fresh‐cut lotus root. The quality characteristics (that is, color, weight loss, texture, pH, polyphenoloxidase activity, and total phenolic content) of the AA + CM‐dipped sample in 100% CO₂ packaging were maintained significantly better than those of the other samples (P < 0.05). The microbiological counts observed in the DW‐dipped sample during storage were higher than those of the AA, CM, and AA + CM samples, and heat‐treatment retarded the microbiological deterioration of fresh‐cut lotus root. Therefore, the results revealed that dipping in an antibrowning treatment (AA + CM), and 100% CO₂ MAP with heat treatment effectively extend the shelf life of fresh‐cut lotus root to 21 d at 5 °C.     

氧化白藜芦醇协同抗坏血酸抑制余甘子酶促褐变的机制研究

通过研究氧化白藜芦醇协同抗坏血酸对余甘子酶促褐变的抑制作用,以及对其多酚氧化酶的酶抑制动力学研究,探明氧化白藜芦醇联合抗坏血酸协同抑制褐变酶的作用机理。结果表明,0.02%氧化白藜芦醇、0.15%抗坏血酸、0.02%氧化白藜芦醇+0.15%抗坏血酸均能减缓余甘子的酶促褐变,对3种褐变酶即多酚氧化酶(PPO)、过氧化物酶(POD)、苯丙氨酸解氨酶(PAL)活性均有较好的抑制作用;0.02%氧化白藜芦醇+0.15%抗坏血酸联合处理对余甘子的酶促褐变及对PPO、POD、PAL的抑制活性强于单独使用。酶抑制动力学结果表明,氧化白藜芦醇对PPO的IC50为(3.300±0.010) μmol/L,抑制机理为可逆的混合型抑制,而氧化白藜芦醇+抗坏血酸(1∶7)的IC50为(1.600±0.020) μmol/L,抑制机理为可逆的竞争性抑制,协同使用导致抑制方式也发生改变。氧化白藜芦醇对PPO的抑制常数KI为0.904 μmol/L,对PPO-底物形成的复合物的抑制常数KIS为14.285 μmol/L,而氧化白藜芦醇+抗坏血酸(1∶7)对PPO的抑制常数KI为0.840 μmol/L,联合处理对PPO的抑制性加强。     

Production of Volatiles in Fresh‐Cut Apple: Effect of Applying Alginate Coatings Containing Linoleic Acid or Isoleucine

One of the main quality parameters in apples is aroma, its main precursors are fatty acids (FA) and amino acids (AA). In this study, alginate edible coatings were used as carriers of linoleic acid or isoleucine to serve as precursors for the production of aroma in cut apples. Apple wedges were immersed in a CaCl₂ solution and coated with one of the following formulations: alginate solution (Alg‐Ca), Alg‐Ca‐low‐level linoleic acid (0.61 g/Lt), (LFA), Alg‐Ca‐high‐level linoleic acid (2.44 g/L; HFA), Alg‐Ca‐low‐level isoleucine (0.61 g/L; LAA), and Alg‐Ca‐high‐level isoleucine (2.44 g/L; HAA). Apple wedges were stored at 3 °C and 85% relative humidity for 21 d and key volatiles were studied during storage. Addition of precursors, mainly isoleucine, showed to increase the production of some key volatiles on coated fresh‐cut apples during storage. The concentration of 2‐methyl‐1‐butanol was 4 times higher from day 12 to day 21 in HAA, while 2‐methyl butyl acetate increased from day 12 to day 21 in HAA. After 21 d, HAA‐apples presented a 40‐fold value of 2‐methyl‐butyl acetate, compared to Alg‐Ca cut apples. Values of hexanal increased during cut apple storage when the coating carried linoleic acid, mainly on HFA, from 3 to 12 d. The ability of apples to metabolize AA and FA depends on the concentration of precursors, but also depends on key enzymes, previous apple storage, among others. Further studies should be done to better clarify the behavior of fresh‐cut apples as living tissue to metabolize precursors contained in edible coatings for the production of volatiles.