Hình 3 .13 Sinh trưởng của các chúng LAB tại các nhiệt độ khác nhau
Hình 3.23 Thành phần tổ hợp khuẩn lạc sau 1 giờ và 4 giờ lên men
(A) thành phần chủng sau 1 giờ lên men
Kết quả định lượng cho thấy tỉ lệ các chủng lactic trong q trình lên men có sự thay đổi. Chủng 3492 chiếm tỉ lệ ngày càng cao, còn tỉ lệ các chủng khác giảm xuống do nhiệt độ 42oC tối ưu hơn cho các chủng thuộc chi Streptococcus >90%. Tuy nhiên về số lượng các chủng, sau 4 giờ đầu đều cho thấy số lượng tăng lên đáng kể. Cụ thể, Số lượng vi sinh vật trong thời gian lên men được trình bày trong bảng sau 3.14. Số lượng vi sinh vật đối với 100ml sữa chua vẫn đạt khoảng 109 CFU, đảm bảo đặc tính probiotic của các chủng này.
Bảng 3.14. Số lượng vi sinh vật trong quá trình lên men.
Thời gian lên men M01 (CFU/ml) 2991(CFU/ml) 3492(CFU/ml)
0 giờ 1,8.107 1,0.107 2,4.107
2 giờ 2,5.107 1,8.107 6,7.107
4 giờ 4,0.107 3,0.107 4,0.108
5giờ 2,2.107 2,5.107 4,8.108
KẾT LUẬN
1. Tuyển chọn và phân loại được 8 chủng vi khuẩn lactic thuộc 2 chi
Lactobacillus và Streptococcus là các chủng an tồn, có khả năng lên men sữa.
2. Các chủng có nhiều đặc tính probiotic tốt, sinh protease, phân giải lactose, có phổ kháng sinh rộng đối với các vi khuẩn gây bệnh thử nghiệm; Có khả năng chịu kháng sinh ở nồng độ thấp. Bốn chủng 2991, La, Ca, 8905 chịu được điều kiện dịch dạ dày, ruột nhân tạo tốt, có tiềm năng sản xuất chế phẩm probiotic. 3. Lựa chọn được 01 tổ hợp 3 chủng (L. bulgaricus M01, L. acidophilus 2991 và S.
thermophilus 3492) có đặc tính probiotic, lên men tạo sản phẩm sữa chua có chất lượng tốt sau 7 giờ lên men, pH 4,44 (±0,02). Chất lượng ổn định sau 3 tuần bảo quản tại 4oC.
4. Các chủng M01, 2991, 3492 sinh trưởng tốt trên môi trường MRS thay thế nguồn C bằng lactose (chủng M01 và 2991) hoặc saccharose (chủng 3492) trong điều kiện nuôi tĩnh, nhiệt độ 35-40oC, pH 6-7.
5. Thử nghiệm lên men sữa thành cơng ở quy mơ 5 lít trong 7 giờ ở nhiệt độ lên men thích hợp là 42oC, tỉ lệ giống 5,0.107 CFU/ml
HƢỚNG NGHIÊN CỨU TIẾP THEO
Thử nghiệm lên men sữa quy mô lớn hơn
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