A Novel Strategy for Minimizing Acid Whey Generation during Greek Yoghurt Production Gangani Uduwerella A thesis submitted in total fulfilment of the requirements of the degree of Master of Science (Research) College of Health and Biomedicine Faculty of Health, Engineering and Science Victoria University 2017 0 Abstract Greek yoghurt is thicker, creamier and surpasses regular yoghurt in terms of protein richness, flavour, texture and taste. Greek yoghurt attains this unique combination by incorporating straining at the end of the production process. However, such straining also generates whey with high lactic acid content, which can cause serious environmental problems unless properly disposed. Difficulties in post-process treatment of this whey stream still presents a main challenge for the industry although various approaches have been attempted. The necessity of developing techniques to reduce the acid whey production are thus importantly emphasized by the dairy industry. This present study aimed to explore an alternative strategy for Greek yoghurt production, which would reduce the amount of acid whey released. The main purpose of whey removal is to obtain desired concentration of total solids in the final Greek yoghurt. The proposed strategy thus aimed to increase the total solid level in initial milk base prior fermentation. This would potentially lead to lower levels of acid whey removal after fermentation. Therefore, the proposed technique would potentially provide a solution to the current acid whey issue. The study applied milk fortification and ultrafiltration techniques as two different approaches to obtain higher dry matter content of the initial milk base. Milk fortification was performed using milk protein concentrate (MPC) and skim milk powder (SMP) to obtain 15%, 20% and 23% w/w dry matter content in the initial milk base. Cloth bag filtering was performed where necessary to obtain a 23% w/w total solid level in yoghurt base. At the second trial, as alternative to milk fortification, ultrafiltration was performed prior fermentation to enhance initial milk total solid levels up to 13% and 17% w/w. Such adjustments were ii investigated from the technological point including starter culture performance, chemical and physical properties of manufactured Greek yoghurt and generated acid whey. A comparison was also made to commercially available products. Addition of MPC and SMP greatly influenced the starter culture activity during fermentation. Protein fortification significantly enhanced the Lb. bulgaricus growth rate and proteolytic activity. Higher solid levels significantly increased the lag phase of St. thermophilus growth due to the effect of osmotic pressure. Greek yoghurt prepared with 23% w/w total solid level, obviously resulted in zero amount of acid whey generation due to total avoidance of filtration after fermentation. However, poor gel structural properties were observed. Best structural properties including higher gel strength and lower syneresis were observed in the Greek yoghurt produced with 20% w/w initial milk total solid compared to manufactured or commercially available products, while acid whey generation was lowered by 47% w/w from typical values of acid whey generated in commonly used commercial processes. Use of the ultrafiltration impacted more on properties of Greek yoghurt compared to milk fortification. Greek yoghurt prepared with 23% w/w total solid level resulted in zero acid whey discharge. However, this yoghurt exhibited inferior structural attributes negatively impacting quality. The Greek yoghurt produced with 20% w/w initial milk total solid level resulted in a 78% w/w reduction in released acid whey compared to the Greek yoghurt made with 15% w/w initial milk total solid. Increased gel hardness, lower syneresis, greater storage modulus for given forces, higher protein and higher fat contents depicted the properties of the Greek yoghurt produced with 20% w/w initial milk total solid. The resulting acid whey in this yoghurt also contained low amounts of lactic acid and Ca, measured to be ~ 0.55% and ~ 0.288% w/w, respectively. The iii present study highlighted that combined use of pre-treating yoghurt base with ultrafiltration prior to fermentation and whey draining after fermentation would result in a yoghurt gel of acceptable physical properties with a concomitant release of very small volume of acid whey. iv Declaration ‘‘I, Gangani Uduwerella, declare that the Master by Research thesis entitled “A Novel Strategy for Minimizing Acid Whey Generation during Greek Yoghurt Production” is no more than 60,000 words in length including quotes and exclusive of tables, figures, appendices, bibliography, references and footnotes. This thesis contains no material that has been submitted previously, in whole or in part, for the award of any other academic degree or diploma. Except where otherwise indicated, this thesis is my own work”. Signature: Date: 03 – July – 2017 (Gangani Uduwerella) v Dedicated to my Parents Sanath, Seetha and my husband Uditha ................. vi Acknowledgements First and foremost, I wish to thank my principle supervisor Professor Todor Vasiljevic, for his expert advice and kind guidance throughout my research. I was very fortunate to work under his supervision and would like to thank him for his time and for giving me the opportunity to work on the interesting research project presented in this MSc thesis. His kind supervision is gratefully acknowledged and I would like to convey my eternal gratitude. I am heartily thankful to my co-supervisor Dr. Jayani Chandrapala, whose continuous guidance truly made my research experience a pleasant one. Her continuous motivation and encouragement not only greatly contributed to the successful completion of my project but also helped me to overcome personal difficulties. Her immeasurable guidance and support is fully appreciated. I would like to thank all the laboratory staff at Victoria University, Werribee especially Stacey Lloid, Joseph Pelle, Charmaine DiQuattro and Sarah Fraser for their technical support during my laboratory experiments. I would like to thank Dairy Innovation Australia and Chr. Hansen for understanding the significance of the project presented in this MSc thesis for dairy industry and facilitating required materials for my laboratory experiments. A very special thank goes to Dr. Muditha Dissanayake, for her generous support from the very first day of my studies until the completion of my studies. Your kind assistance, technical support and motivation helped me immensely. vii I appreciate the great friendships I have made during my research studies at Victoria University specially, Manjula Nishanthi, Rangani Wijayasinghe, Chathuri Piyadasa, Nuwan Vithanage, Samantha Liyanarachchi, Dimuthu Bogahawaththa, Kasup Munaweera, Manpreet Grewal among others. I would like to thank them for their kind friendship and pleasant company. I sincerely thank my parents for their love, care and guidance throughout my life. I would also like to thank my brother Aruna, sister Chinthani and their families for supporting me in every aspect. Their support and encouragement have been the driving force throughout my life. Finally, my deepest gratitude goes to my husband Uditha for his unflagging love and unconditional support throughout my life and my studies. Without his love, and encouragement, I would never have finished this thesis. viii Contents 1. Introduction .................................................................................................................. 1 1.1 Background ......................................................................................................... 2 1.2 Research Aim and Objectives ............................................................................. 5 1.3 Structure of the thesis ......................................................................................... 6 2. Literature review........................................................................................................... 8 2.1 Evolution of Greek yoghurt ................................................................................ 9 2.2 Milk as the Main Ingredient .............................................................................. 11 2.2.1 Proteins ....................................................................................................... 11 2.2.2 Fat ............................................................................................................... 14 2.2.3 Carbohydrates – Lactose ............................................................................ 15 2.2.4 Minerals ...................................................................................................... 15 2.3 Greek yoghurt production process .................................................................... 16 2.3.1 Standardization ........................................................................................... 17 2.3.2 Homogenization ......................................................................................... 20 2.3.3 Pasteurization ............................................................................................. 22 2.3.4 Fermentation .............................................................................................. 23 2.3.5 Filtration ..................................................................................................... 32 2.4 Acid whey ........................................................................................................