酶法水解乳糖与热处理偶联对牛乳Maillard反应的影响

旨在探讨乳糖水解程度及热处理方法与Maillard反应的关系,鲜牛乳用中性乳糖酶处理获得不同水解程度的低乳糖牛乳,然后对牛乳进行不同的热处理,处理后的样本进行Maillard反应程度评价。采用葡萄糖氧化酶法测定不同水解时间的牛乳中葡萄糖质量浓度和乳糖水解率,用高效液相色谱法和紫外分光光度法分别测定水解后牛乳经不同热处理后的糠氨酸和5-羟甲基糠醛(5-hydroxymethylfurfural,5-HMF)含量及牛乳褐变程度的OD值。结果表明,随着乳糖水解时间的延长,牛乳中的葡萄糖含量呈增加的趋势,葡萄糖质量浓度从0.00 mg/100 m L增加到1 721.33 mg/100 m L,但增加趋势逐渐变缓;乳糖水解率从0%增加到70.33%,水解时间2.0 h后的牛乳水解率达到了50%以上。糠氨酸含量呈上升的趋势(P0.05),水解时间在3.0 h以上并经75℃、30 min热处理的牛乳,糠氨酸含量超过了190 mg/100 g pro;水解时间为0.5 h及以上并经75℃、15 s热处理的牛乳,糠氨酸含量超过了12 mg/100 g pro。生鲜牛乳和水解后经75℃、30 min热处理的牛乳,均未检测到5-HMF,水解后经75℃、15 s热处理的牛乳,随乳糖水解时间的延长,牛乳中5-HMF含量增加显著(P0.05)。牛乳的褐变程度随乳糖水解时间显著增加(P0.05),且乳糖酶水解后75℃、30 min热处理的牛乳的褐变程度明显高于75℃、15 s热处理的牛乳。本研究结果说明,乳糖经过酶水解后的牛乳,长时间热处理会加重乳Maillard反应,影响乳的蛋白质品质。

Effect of Enzymatic Hydrolysis of Lactose Combined with Heat Treatments on Maillard Reaction of Milk

The objective of this study was to investigate the relationship between the hydrolysis degree of lactose combined with heat treatments and Maillard reaction in milk. Fresh milk was hydrolyzed with neutral lactase to obtain low-lactose milk with different hydrolysis degrees. Then, the products were treated by various heating methods and the degree of Maillard reaction was assessed. The glucose concentration and the hydrolysis degree of lactose in milk at different hydrolysis times were measured by the glucose oxidase method. Furosine and 5-hydroxymethylfurfural (5-HMF) contents and browning degree (OD values) were determined by using high-performance liquid phase chromatography (HPLC) and ultraviolet spectrophotometry, respectively. The results showed that the glucose content in milk was increased with prolonged time of lactose hydrolysis, and glucose concentration slowly increased from 0.00 to 1 721.33 mg /100 mL. Similarly, lactose hydrolysis percentage increased from 0% to 70.33%, reaching a level higher than 50% after 2.0 h heat treatment. Furosine content in milk showed a rising trend with extended heat treatment (P < 0.05). Milk subjected to hydrolysis for more than 3.0 h and then heat treatment at 75 ℃ for 30 min had a furosine content exceeding 190 mg/100 g protein, while hydrolysis for 0.5 h and longer followed by heat treatment at 75 ℃ for 15 s resulted in a furosine content more than 12 mg/100 g protein. 5-HMF was not detected in fresh milk or in milk hydrolyzed and heat treated at 75 ℃ for 30 min. The content of 5-HMF in hydrolyzed milk increased with the extension of hydrolysis time followed by heat treatment at 75 ℃ for 15 s (P < 0.05). Likewise, the browning degree significantly increased with the extension of hydrolysis time (P < 0.05). Browning reaction in milk treated at 75 ℃ for 30 min was significantly higher than that at 75 ℃ for 15 s. Therefore, enzymatic hydrolysis of lactose coupled with heat treatment can promote Maillard reaction and thus affect protein quality in milk.