Venkatachalam Karthikeyan, Charoenphun Narin, Lekjing Somwang, Noonim Paramee
Faculty of Innovative Agriculture and Fishery Establishment Project, Prince of Songkla University, Surat Thani Campus, Makham Tia, Mueang, Surat Thani 84000, Thailand.
Faculty of Science and Arts, Burapha University Chanthaburi Campus, Chanthaburi 22170, Thailand.
Foods. 2023 Dec 24;13(1):72. doi: 10.3390/foods13010072.
Longkong ( Griff.) fruit is prone to rapid pericarp browning and shortened shelf life (<7 days) under prolonged low-temperature storage. This study investigates the effect of an edible coating, comprising carboxymethyl cellulose (CMC) and gelatin in a fixed 3:1 ratio, integrated with various concentrations of melatonin (MT) (0.4, 0.8, and 1.2 mM/L) to mitigate chilling injury in longkong fruit. Coated longkong fruits were stored at 13 °C with 90% relative humidity for 18 days and underwent physicochemical evaluations every three days. Samples coated with CMC-Gel without MT and uncoated fruits were served as controls. The findings indicated that the CMC-Gel-MT coating significantly mitigated pericarp browning, chilling injury, weight loss, and respiration rate increase under extended cold storage conditions. High concentrations of MT (≥0.8 mM/L) in the coating notably inhibited the activities of cellular degrading enzymes such as lipoxygenase and phospholipase D. This inhibition contributed to reduced membrane permeability, lower reactive oxygen species accumulation (HO, OH, O), and decreased malondialdehyde levels in the longkong pericarp. Furthermore, the CMC-Gel-MT coating increased the activity of phenylalanine ammonia lyase, leading to an enhancement in phenolic content. Consequently, it improved the fruit's ability to scavenge DPPH (2,2-diphenyl-1-picrylhydrazyl) and ABTS (2,20-azino-di-3-ethylbenzthiazoline sulfonic acid) radicals. Control samples exhibited high levels of pericarp browning-related enzymes (polyphenol oxidase, peroxidase), whereas CMC-Gel-MT-coated fruits, particularly at higher MT concentrations, showed significant reductions in those enzyme activities. In conclusion, incorporating high concentrations of MT in a CMC-Gel-based edible coating is a promising alternative for mitigating chilling injury in longkong fruit.
龙眼（Griff.）果实长时间低温贮藏时，果皮容易迅速褐变，货架期缩短（<7天）。本研究考察了以固定比例3:1的羧甲基纤维素（CMC）和明胶组成的可食性涂膜，并添加不同浓度褪黑素（MT）（0.4、0.8和1.2 mM/L）对减轻龙眼果实冷害的效果。涂膜后的龙眼果实于13℃、相对湿度90%条件下贮藏18天，每3天进行一次理化评价。以未添加MT的CMC-明胶涂膜果实和未涂膜果实作为对照。结果表明，在延长冷藏条件下，CMC-明胶-MT涂膜显著减轻了果皮褐变、冷害、失重和呼吸速率增加。涂膜中高浓度MT（≥0.8 mM/L）显著抑制了脂氧合酶和磷脂酶D等细胞降解酶的活性。这种抑制作用有助于降低龙眼果皮的膜透性、减少活性氧积累（HO、OH、O）以及降低丙二醛水平。此外，CMC-明胶-MT涂膜提高了苯丙氨酸解氨酶的活性，导致酚类含量增加。因此，它提高了果实清除2,2-二苯基-1-苦基肼（DPPH）和2,2'-联氮-双-3-乙基苯并噻唑啉-6-磺酸（ABTS）自由基的能力。对照样品表现出高水平的与果皮褐变相关的酶（多酚氧化酶、过氧化物酶），而CMC-明胶-MT涂膜果实，尤其是MT浓度较高时，这些酶的活性显著降低。总之，在基于CMC-明胶的可食性涂膜中加入高浓度MT是减轻龙眼果实冷害的一种有前景的方法。
