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ORIGINAL RESEARCH

Stability of Instant Coffee Foam by Nanobubbles Using Spray-Freeze Drying Technique Shweta M. Deotale 1 & Sayantani Dutta 1 & J. A. Moses 1 & C. Anandharamakrishnan 1 Received: 30 April 2020 / Accepted: 8 September 2020 # Springer Science+Business Media, LLC, part of Springer Nature 2020

Abstract Instant coffee with stable foam is considered to be an important parameter for consumer preference and acceptability. For foam sustenance, nanoscale bubbles are more useful compared with microbubbles, due to their high specific area and high stagnation in the liquid phase (without undesirable liquid drainage). The technique that produces nanobubbles in coffee would concomitantly produce and preserve the coffee foam, the best. Spray-freeze drying (SFD) is known to be more effective for the production of instant coffee, compared with conventional spray drying (SD) and freeze drying (FD) techniques. However, its efficiency in the production of nanobubbles has not been explored. To address the issue, in the present study, SFD has been employed to produce instant coffee, and the findings have been compared with SD and FD. The coffee powder obtained with SFD produced a foam with higher stability that also comprised of nanobubbles, in contrast to SD and FD powders. The FE-SEM analysis of SFD foam showed the presence of nanobubbles in the range of 100–200 nm. When the beverage was prepared, the SFD coffee powder dissolved in water at 90 °C produced an excellent foam. The said foam structure was intact up to 2400 s (40 min), and lost only 89.5 ± 2 mm of foam height, during the experiment. Thus, apart from instant coffee, a stable foam in coffee comprising nanobubbles can also be achieved through the SFD. Keywords Spray-freeze drying . Nanobubbles . Coffee . Foam stability . Foam structure

Introduction Spray-freeze drying (SFD) is a unique drying technique that amalgamates two conventional drying methods of spray drying (SD) and freeze drying (FD), overcoming their limitations, and bringing out the best from both. It is an effective preservation technique for biologicals, volatiles, and food supplements. It protects them from environmental challenges, as well as decrease the drying time (Dutta et al. 2018; Karthik and Anandharamakrishnan 2013). Ishwarya and Anandharamakrishnan (2015) have established the supremacy of SFD over SD and FD for the production of instant coffee. These researchers have proven that the coffee Shweta M. Deotale and Sayantani Dutta contributed equally to this work. * C. Anandharamakrishnan [email protected] 1

Computational Modeling and Nanoscale Processing Unit, Indian Institute of Food Processing Technology (IIFPT), Ministry of Food Processing Industries, Government of India, Thanjavur, Tamil Nadu 613005, India

powder obtained by SFD possesses an improved product quality, in terms of aroma and powder characteristics, compared with SD and FD coffee powders (Ishwarya and Anandharamakrishnan 2015). However, a study on the foam obtained from the SFD coffee powder in the beve