ORIGINAL RESEARCH Effect of sonication conditions: Time, temperature and amplitude on physicochemical, textural and sensory properties of yoghurt REZA ESMAEILZADEH KENARI and RAZIE RAZAVI * Department of Food Science and Technology, Sari Agricultural Sciences and Natural Resources University, Km 9 of Sea Road, Sari, Mazandaran 48181-68984 Iran The influence of sonication conditions (amplitude of ultrasound probe = 50, and 75%, time = 5, 10 and 15 min and temperature = 45, 55 and 65 °C) on the properties of yoghurt was investigated. The apparent viscosity, hardness and lightness increased when sonication time, temperature and amplitude increased. At 75% of amplitude, the pH, syneresis and flavour decreased but acidity, adhesiveness, cohesiveness, springiness, chewiness, redness, yellowness and overall acceptance increased. As the sonication temperature increased, acidity, syneresis, adhesiveness and yellowness decreased. Based on the physicochemical and sensorial results, sonication at 55 °C, 10 min and 75% of amplitude, effectively improved the properties of yoghurt. Keywords Colour, Milk gel, Texture, Nonthermal processing, Ultrasound, Syneresis, Viscosity. INTRODUCTION Fermented dairy products like yoghurt are con- sidered suitable carriers to deliver nutritional constitutes such as calcium, phosphorus, potas- sium, magnesium, vitamin A, B 2 and B 12 , high biological value proteins, essential fatty acids and probiotics (Hadjimbei et al. 2020), required for growth, health, bone strength and energy (Mohd Khairi et al. 2018; Scudino et al. 2020). The consumption of yoghurt, one of the most consumed and widely accepted functional fer- mented foods in the world (Hadjimbei et al. 2020), has been linked with important health benefits, including the improvement of gut microbiota, reduced lactose intolerance symp- toms, improved immune responses, improved gastrointestinal functionality, and may prevent osteoporosis, diabetes and cardiovascular dis- eases (Alizadeh Khaledabad et al. 2020; Had- jimbei et al. 2020; ). The demand of the global market for new products that meet the expectations and needs of modern consumers had led various industrial sections to invest in innovations in their prod- ucts and processes (Monteiro et al. 2018). The common process of yoghurt production is pre- treatment, milk standardisation for fat and dry matter, homogenisation, thermal processing, inoculation with starter culture, fermentation and cooling (Erkaya et al. 2015). The conventional heat treatments possess negative effects of heat- ing on the nutritional characteristics of products (degradation of vitamin and lactose) and alter organoleptic properties (texture, off-flavour for- mation and colour) of the processed products (Ahmad et al. 2019; Guimar ˜ aes et al. 2019; Scudino et al. 2020). It also requires high amounts of energy, which affects the cost of the final product and the profitability of the dairy industry (Ahmad et al. 2019; Balthazar et al. 2019). Nowadays, demand for minimally processed, healthy, safe and high-quality food products pro- duced by using new technologies like nonther- mal processing, which has less adverse effects on the nutritional value of products has been ris- ing (Erkaya et al. 2015; Ahmad et al. 2019; Balthazar et al. 2019). Most of the negative effects of thermal treatment can be reduced by using nonthermal technologies, thus resulting in food products with improved quality (Ahmad et al. 2019). Ultrasonication, irradiation, high- pressure technology, cold plasma technology, electrical pulse field and microfluidisation are various nonthermal techniques for milk *Author for correspondence. E-mail: razavirazie@yahoo.com © 2021 Society of Dairy Technology 332 Vol 74, No 2 May 2021 International Journal of Dairy Technology doi: 10.1111/1471-0307.12761