Structure modification of sour milk products by transglutaminase

Kirsi Rajakari

    Research output: ThesisDoctoral ThesisMonograph


    The dairy food sector traditionally utilizes enzymes such as rennet. To date, novel crosslinking enzymes, including transglutaminase (TG; EC, have not been widely applied in the dairy industry. Microbial TG is a transferase which forms both inter- and intramolecular isopeptide bonds between glutamine and lysine amino acids. It forms bonds between similar proteins and caseins that are good substrates for TG. The first investigation of TG in yogurt was published approximately 14 years ago. TG has been mostly studied in set yogurts and stirred yogurts. A few studies of TG in kefir have been published, but studies of fermented milk and viili are lacking. In traditional manufacturing methods for sour milk products, a high protein content is needed to obtain a viscous and firm structure. This incurs additional costs. In this work, the economical manufacturing methods utilized for sour milk products were developed with the aid of TG. In yogurt production, the protein content was decreased by 12%. High-pressure homogenization at 400 bar significantly improved yogurt viscosity, which was 57% more viscous than traditionally homogenized (230 bar) and TG-treated yogurt. In fermented milk production, the protein content was decreased by 9%. The formation of flakes was avoided with a preincubation step. In viili production, the protein content was decreased by 25%. The lower protein level in yogurt, fermented milk and viili production could be achieved without any loss of viscosity or firmness and sensory properties. Commercial TG products are powders which are difficult to dose at factory scale because of the high pressure in the tanks, which creates dust. This dust might result in allergies in employees. This thesis describes a method to produce a novel liquid form of TG, which maintains its activity and microbial quality. This liquid TG was compared to powdered TG in the production of yogurt. Liquid TG was extremely stable at -20 °C for 6.5 months. The powdered TG and liquid TG were equally efficient in the production of yogurt. The viscosity of both yogurts was approximately 70 mPas. The present study demonstrates that high-quality sour milk products can be manufactured with liquid TG and high pressure homogenization.
    Translated title of the contributionHapanmaitotuotteiden rakenteen muokkaaminen transglutaminaasilla
    Original languageEnglish
    QualificationDoctor's degree
    Awarding Institution
    • Aalto University
    • Ojamo, Heikki, Supervising Professor
    • Myllärinen, Päivi, Thesis Advisor, External person
    Print ISBNs978-952-60-6183-2
    Electronic ISBNs978-952-60-6184-9
    Publication statusPublished - 2015
    MoE publication typeG4 Doctoral dissertation (monograph)


    • transglutaminase
    • structure
    • sour milk products
    • yogurt
    • fermented milk
    • viili


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