Hung Hsiao-Ying, Hsu Yu-Yun, Su Pei-Fang, Chang Ying-Ju
Department of Nursing & Institute of Allied Health Sciences, College of Medicine, National Cheng Kung University, No. 1, Daxue Rd., East Dist., Tainan, Taiwan.
Department of Statistics, National Cheng Kung University, Tainan, Taiwan.
BMC Pediatr. 2018 Mar 2;18(1):94. doi: 10.1186/s12887-018-1075-1.
Human breastmilk provides the best nutrition for infants. When women or infants have difficulties in breastfeeding directly, breastmilk is usually pumped and frozen for later use. However, while frozen, breastmilk may develop a rancid flavor, which induces infant feeding stress and raises the mothers' concerns about the quality of frozen breastmilk. Nevertheless, few studies have investigated the variations in the compounds that cause the rancid flavor of breastmilk during frozen storage.
A repeated-measures design was adopted to quantify the variations in rancid-flavor compounds, namely acid value (AV), total free fatty acids (FFAs), and short-and intermediate-chain FFAs of breastmilk during frozen storage. Breastmilk was obtained from ten healthy mothers of full-term infants and each milk sample was divided into three aliquots: fresh, 7-day frozen and 30-day frozen samples. The fresh samples were immediately analyzed, while the others were frozen in a domestic fridge within a temperature range of -15 to -18 °C and analyzed 7 and 30 days later.
The rancid-flavor compounds of the breastmilk, namely AV, total FFAs and intermediate-chain FFAs, significantly increased with storage time, all of which reached the sensory threshold for detecting the rancid flavor of milk. In addition, the FFAs of the breastmilk samples frozen for 7 days far exceeded the detection threshold for unpleased rancid flavor, while the 30-day samples were higher than the intolerable level for most people.
This study revealed that the human breastmilk develops a rancid flavor during frozen storage. Therefore, we recommend that when infants refuse thawed milk, mothers can try to provide freshly expressed milk whenever possible or provide breastmilk frozen for less than 7 days. Future studies could explore the methods for slowing breastmilk lipolysis to maintain its fresh flavor.
人乳为婴儿提供了最佳营养。当母亲或婴儿在直接母乳喂养方面存在困难时，通常会将母乳挤出并冷冻以备后用。然而，冷冻期间，母乳可能会产生酸败味，这会导致婴儿喂养困难，并增加母亲对冷冻母乳质量的担忧。尽管如此，很少有研究调查冷冻储存期间导致母乳产生酸败味的化合物的变化情况。
采用重复测量设计来量化冷冻储存期间母乳中酸败味化合物的变化，即酸值（AV）、总游离脂肪酸（FFA）以及短链和中链FFA。从10位足月婴儿的健康母亲处获取母乳，每个母乳样本分为三份：新鲜样本、冷冻7天的样本和冷冻30天的样本。新鲜样本立即进行分析，其他样本在温度范围为-15至-18°C的家用冰箱中冷冻，并在7天和30天后进行分析。
母乳中的酸败味化合物，即AV、总FFA和中链FFA，随储存时间显著增加，所有这些都达到了检测牛奶酸败味的感官阈值。此外，冷冻7天的母乳样本中的FFA远远超过了不愉快酸败味的检测阈值，而冷冻30天的样本高于大多数人的耐受水平。
本研究表明，人乳在冷冻储存期间会产生酸败味。因此，我们建议，当婴儿拒绝解冻后的母乳时，母亲可以尽可能尝试提供新鲜挤出的母乳，或者提供冷冻时间少于7天的母乳。未来的研究可以探索减缓母乳脂肪分解以保持其新鲜风味的方法。
