Method for preparing a dairy product having a stable content of galacto-oligosaccharide(s)
The present invention describes a process for in situ generation of stable GOS in different dairy products by the use of a transgalactosylating β-galactosidase.
1. A method of treating a galacto-oligosaccharides containing milk-based substrate, wherein said milk-based substrate comprises β-galactosidase wherein said β-galactosidase is Bifidobacterium derived β-galactosidase having transgalactosylating activity, which method comprises the step of heat treating said milk-based substrate at a temperature (T) in the range of 90° C.-130° C. for a period of time of at least x seconds, wherein x is related to the temperature T by: x=153,377,215,802.625 e −20378144T ; to obtain a heat treated dairy product, wherein the variation in content of galacto-oligosaccharides is within 0.4% (w/v) in a period of at least 14 days.
2. The method according to claim 1 , wherein said method before said heat treating step further comprises a step of in situ enzymatic treatment of said milk-based substrate with said β-galactosidase to obtain said galacto-oligosaccharides containing milk-based substrate.
3. The method according to claim 1 , wherein said β-galactosidase has a ratio of transgalactosylation activity above 100%.
4. The method according to claim 1 , wherein said temperature is a temperature in the range of 90° C.-119° C.
5. The method according to claim 1 , wherein said period of time is in the range of 0.01 second to 1300 seconds.
6. The method according to claim 1 , wherein the variation in content of galacto-oligosaccharides is within 0.4% (w/v) in a period of at least 3 weeks.
7. The method according to claim 1 , wherein the amount of galacto-oligosaccharide in said heat treated dairy product is within 0.5 to 10% (w/v).
8. The method according to claim 1 , wherein said dairy product has below 0.0213-LAU/ml of residual β-galactosidase activity.
9. The method according to claim 1 , wherein the variation in content of galacto-oligosaccharide is within 0.25% (w/v) measured over at least 14 days.
10. The method according to claim 1 , wherein said milk-based substrate comprises lactose in an amount of at least 1% (w/v).
11. The method according to claim 1 , wherein the Bifidobacterium derived β-galactosidase is a Bifidobacterium bifidum derived β-galactosidase comprising an amino acid sequence having at least 90% sequence identity with an amino acid sequence selected from the group of SEQ ID NO: 1, SEQ ID NO: 2, and SEQ ID NO: 3; and/or wherein the Bifidobacterium derived β-galactosidase is a polypeptide having the amino acid sequence selected from the group of SEQ ID NO: 1, SEQ ID NO: 2 and SEQ ID NO: 3; and/or wherein the Bifidobacterium derived β-galactosidase is a polypeptide comprising any of the polypeptides selected from the group consisting of SEQ ID NO: 1, SEQ ID NO: 2, and SEQ ID NO: 3; and/or wherein the Bifidobacterium derived β-galactosidase is a truncated fragment of any of the polypeptides selected from the group consisting of SEQ ID NO: 1, SEQ ID NO: 2, and SEQ ID NO: 3, and having a minimum length of 850 amino acid residues.
12. The method according to claim 11 , wherein the Bifidobacterium derived β-galactosidase comprises a polypeptide selected from the group consisting of: a. a polypeptide comprising an amino acid sequence having at least 90% sequence identity with SEQ ID NO: 1, wherein said polypeptide consists of at most 980 amino acid residues, b. a polypeptide comprising an amino acid sequence having at least 97% sequence identity with SEQ ID NO: 2, wherein said polypeptide consists of at most 975 amino acid residues, c, a polypeptide comprising an amino acid sequence having at least 96.5% sequence identity with SEQ ID NO: 3, wherein said polypeptide consists of at most 1300 amino acid residues.
13. The method according to claim 11 , wherein the dairy product is drinking milk, sweet milk, condensed milk, whey, or a fermented dairy product.
14. The method according to claim 13 , wherein the dairy product is a fermented dairy product selected from the group consisting of yogurt, buttermilk, Riazhenka, cheese, creme fraiche, quark, Acidophilus milk, Leben, Ayran, Kefir, Sauermilch and fromage frais.