Ultra high temperature (UHT) processability of high protein dispersions prepared from milk protein-soy protein hydrolysate mixtures

Highlights

• Milk protein concentrate (80 g/kg) could be processed at ultra high temperature.

• Similar behaviour was shown by soy protein hydrolysate.

• Soy-milk protein mixes showed reduced ultra high temperature processability.

• Soy Peptides increased the aggregation and coagulation of milk proteins.

Abstract

This study investigated the effect of addition of soy protein hydrolysates on Ultra high temperature (UHT) processability of milk protein beverages. There is also a lack of reported data on UHT processability of soy protein hydrolysates. UHT processability of 80 g/kg protein reconstituted milk protein concentrate (8-RMPC), 80 g/kg protein soy protein hydrolysate (8-RSPH) and 8-RMPC with added 10, 20 and 30 g/kg protein RSPH (e.g. 8-RMPC+1-RSPH) was studied on a bench-top UHT equipment. Both 8-RMPC and 8-RSPH showed very high UHT processability (UHT plant run-time > 120 min). Inclusion of 1-RSPH in 8-RMPC did not affect UHT run-time (>120 min) and overall heat transfer coefficient (OHTC). Significant drop in OHTC was observed in 8-RMPC+2-RSPH without reducing the UHT run-time below 120 min mark and required UHT processing temperatures could be maintained (143–146 °C) throughout the UHT run. 8-RMPC+3-RSPH showed markedly reduced UHT processability both shorter UHT run-time (61 min) and very low OHTC values were observed which can be attributed to formation of larger protein aggregates. An increase in apparent viscosity (42.0 ± 0.6 and 11.8 ± 0.3 mPa s) for 8-RSMP+3-RSPH and 8-RSMP+2-RSPH, respectively) of UHT processed samples would have also induced severe fouling during UHT.

Introduction

Incorporation of high quality proteins in human diet is positively related to muscle gain, losing weight and controlling diabetes (Etzel, 2004). Additionally, peptides derived from hydrolysis of dietary proteins are often shown to have antihypertensive, anti-inflammatory, immunomodulatory, antioxidant, antimicrobial and various other bioactive functions in human body (Maestri, Marmiroli, & Marmiroli, 2016; Nielsen, Beverly, Qu, & Dallas, 2017). There has been an ongoing interest in the production and incorporation of peptide ingredients in food product formulation due to their bioactivity (Chalamaiah, Yu, & Wu, 2018; Li-Chan, 2015; Toldrá, Reig, Aristoy, & Mora, 2018). Apart from health benefits, researchers have also shown that controlled hydrolysis of proteins can enhance their functional properties; such as solubility and emulsifying properties when compared to native proteins (Barać, Stanojević, Jovanović, & Pešić, 2004).

High protein beverages are a convenient source of protein to meet a large amount of daily recommended protein intake. These products are commonly manufactured using milk proteins and to a lesser extent plant proteins (Sethi, Tyagi, & Anurag, 2016). A growth in consumption of plant proteins and plant protein fortified beverages has been observed (Lan, Chen, & Rao, 2018). Soy protein is arguably one of the most popular plant based protein used in food industry (Hettiarachchy & Kalapathy, 1997). Soy proteins, similar to milk proteins contain all of the essential amino acids vital for human nutrition (Hettiarachchy & Kalapathy, 1997). Soy protein based beverages, however are not a very popular consumer choice as compared to dairy protein based beverages in western countries, owing to their undesirable sensory properties, such as unfavourable beany flavour profile (Beliciu & Moraru, 2011; Singh, Kumar, Sabapathy, & Bawa, 2008). There are also concerns about adverse effects of isoflavones present in soy based products on male reproductive function. The soy isoflavones can behave like an endocrine disrupting chemical (Nardi et al., 2017). There has been several studies carried out on addition of low amounts of soy proteins in dairy products such as low fat ice-cream and yogurt (Biswas, Chakraborty, & Choudhuri, 2002; Friedeck, Aragul-Yuceer, & Drake, 2003). Similarly, small but dietary significant amounts of soy protein ingredients can be added to milk protein beverages (Singh et al., 2008).

Ultra high temperature (UHT) technology is a preferred mode of processing neutral pH high protein beverages to produce a commercially sterilize shelf-stable product with minimal thermal damage to nutrients and sensory attributes (Beecher, Drake, Luck, & Foegeding, 2008; Burton, 1994). However, there are concerns about formation of deposit layers of protein and other constituents on heat exchanger surfaces. This fouling of surfaces results in decreased processing run times, requiring frequent down times for cleaning in place operations (Burton, 1994).

In the present work milk protein concentrate (MPC) was used as a main ingredient for formulating milk protein-soy protein dispersions, a decision based on a previous work showing high UHT processability of reconstituted MPC (RMPC) (Singh, Prakash, Bhandari, & Bansal, 2019). MPC is an excellent form of concentrated milk protein ingredient, which can be used to formulate neutral pH (pH ~ 6.8) high protein beverages (Banach, Lin, & Lamsal, 2013). Soy protein ingredients are available as soy protein concentrate, soy protein isolate and soy protein hydrolysate. Soy protein hydrolysates have superior solubility as compared to non-hydrolysed soy protein isolates (Ortiz & Wagner, 2002; Panyam & Kilara, 1996). Solubility is considered as one of the most important factors when selecting a protein ingredient for beverage mix (Jideani, 2011; Phillips, Whitehead, & Kinsella, 1994). The enzyme hydrolysis of a protein can improve its solubility by increasing the protein-water interactions due to the formation of charged peptides with COO⁻ and NH³⁺ groups, however, it can also expose hydrophobic groups (Tavano, 2013). Due to this, the addition of hydrolysed proteins in MPC can affect its UHT processability due to undesirable protein-peptide interactions affecting its fouling behaviour. Hence, a model system is needed to study the interactions between these two different types of proteins.

Most of the research work on the UHT processing of soy products has been carried out on soy milk (Durand, Franks, & Hosken, 2003; Kwok, Liang, & Niranjan, 2002). There is a lack of reported data on UHT processability of soy protein ingredients and their compatibility with milk proteins during thermal processing. The present work addressed this issue and was designed to gain insights into the effect on UHT processability and fouling behaviour of mixed protein systems.