Lactose-Hydrolyzed Milk Is More Prone to Chemical Changes during Storage than Conventional Ultra-High-Temperature (UHT) Milk

Abstract

The enzymatic hydrolysis of lactose to glucose and galactose gives rise to reactions that change the chemistry and quality of ambient-stored lactose-hydrolyzed ultra-high-temperature (UHT) milk. The aim of the present study was to investigate and compare chemical changes in lactose-hydrolyzed and conventional UHT milk during a 9 month ambient storage period. Several complementary analyses of volatiles, free amino acids, acetate, furosine, and level of free amino terminals were concluded. The analyses revealed an increased level of free amino acids and an increased formation rate of specific compounds such as furosine and 2-methylbutanal in lactose-hydrolyzed UHT milk compared to conventional UHT milk during storage. These observations indicate more favorable conditions for Maillard and subsequent reactions in lactose-hydrolyzed milk compared to conventional UHT milk stored at ambient temperature. Furthermore, it is postulated that proteolytic activity from the lactase-enzyme preparation may be responsible for the observed higher levels of free amino acids in lactose-hydrolyzed UHT milk.

Pasteurised, microfiltered and lactose‐hydrolysed skimmed milk with added probiotics: Development and storage stability

“…According to Jansson et al . (), lactose hydrolysis can be associated with increases in the proteolytic activity of the milk, probably due to the proteolytic side effects of the added lactase enzyme preparation. In that paper, they observed an important increase in free amino acids and free amines in the UHT lactose‐hydrolysed milks, as compared to conventional UHT milk.…”

“…Moreover, the higher proteolytic activity in lactose‐hydrolysed milk increases the level of free amino terminals and amino groups from lysine on the side chain, which may also contribute to the Maillard reaction and loss of availability of lysine, and therefore, the nutritional value of the protein may be lower in this type of milk (Jansson et al . ). As a consequence, these UHT lactose‐hydrolysed milk products tend to darken in colour, which could also prejudice their acceptability, especially when consumed alone.…”

Proteolysis Process in Fermented Sausage Model Systems As Studied by NMR Relaxometry

“…Degree of proteolysis was estimated by measurement of free amino terminal groups using the fluorescamine assay described earlier. 22 One hundred milligrams of each sample was solubilized in 1 mL of phosphate-buffered saline (0.05 M phosphate buffer, 0.14 M NaCl, pH 6.7). To 500 μL of 1.67 M (24%) trichloroacetic acid in water was added an equal volume of solubilized sample, and the mixture was held for 20 min on ice to allow precipitation of intact proteins.…”

Isıl İşlem Görmüş İçme Sütlerinde (Pastörize, UHT ve Laktozsuz UHT Süt) Hidroksimetilfurfural İçeriğinin Belirlenmesi

“…Laktozsuz sütlerde laktozun enzimatik hidrolize uğrayarak glikoz ve galaktoza dönüşmesi, aminlerle (proteine bağlı lisin ve diğer NHuçları) daha yüksek reaktivite göstermesine yol açarak Maillard reaksiyonu için daha uygun bir ortam oluşturmaktadır [16,17]. Ayrıca, laktozsuz sütlere ilave edilen laktaz enziminin de proteolitik aktiviteler gibi istenmeyen uç aktiviteler ile serbest aminoasit miktarında artışa neden olarak reaksiyonu etkilediği bildirilmiştir [16]. Literatürde ısıl işlem görmüş sütlerin HMF oranlarına dair kısıtlı sayıda çalışma bulunmakla birlikte, laktozsuz sütlerin HMF değerlerine ilişkin bir çalışmaya rastlanılmamıştır.…”

“…Literatürde ısıl işlem görmüş sütlerin HMF oranlarına dair kısıtlı sayıda çalışma bulunmakla birlikte, laktozsuz sütlerin HMF değerlerine ilişkin bir çalışmaya rastlanılmamıştır. Ancak, laktozun hidrolizasyonuyla ortaya çıkan indirgen şekerlerin Maillard reaksiyonunu hızlandırdığı, diğer ısıl işlem indikatörleri olan laktuloz ve furosin miktarları belirlenerek ortaya konulmuştur [16,[18][19][20].…”