035: Evaluation of the Processability of Dry-Heat-Treated Skim Milk Powder Into Natural Cheese

Introduction

Skim milk powder (SMP) is an important auxiliary ingredient in dairy production, which plays a role in adjusting and strengthening the milk solids content of raw material milk. While SMP is mainly used in beverages and yogurt, it is rarely used in natural cheese production. The main reason why SMP is not used as a cheese ingredient is that the rennet-induced gelation and gel syneresis during cooking are poorer in SMP compared to low-heat-pasteurized milk. In our previous research, we found that dry-heat treatment of SMP increased the surface hydrophobicity of casein. Since hydrophobic interactions between proteins are important for rennet-induced gelation and gel syneresis, it was thought that dry-heat treatment of SMP would increase the surface hydrophobicity of casein, thereby improving its processability into natural cheese. In this study, we investigated the processing ability of dry-heat-treated SMP into natural cheese, focusing on the rennet-induced gelation and gel syneresis during cooking.

Methods

Low-heat SMP (pasteurization temperature: 65°C, 30 min) was produced from raw milk obtained from a farm attached to the Tokyo University of Agriculture. SMP was dry-heat treated at 65°C, relative humidity 40% for 9 h. Dry-heat-treated SMP was reconstituted with Milli-Q water (protein concentration: 4%), and rennet was added to a final concentration of 0.018 IMCU/mL. 5 mL of the mixture was incubated at 32°C to prepare a rennet-induced gel. The strengths of the prepared gels were measured via rupture tests. Gel syneresis was analyzed by measuring the weight of water released when the gels were cooked in a 40°C water bath.

Results

Rennet-induced gel strength of dry-heat-treated SMP was increased by about 1.5 times compared to that of untreated SMP. In addition, the gel strength of dry-heat-treated SMP was almost the same as that of low-heat pasteurized milk. Furthermore, analysis of gel syneresis showed that the amount of water released during cooking increased by about 10% in dry-heat-treated SMP compared to untreated SMP. These results suggested that dry-heat treatment of SMP improves its processability into natural cheese.

Significance

This study provides new insights into the use of SMP in natural cheese production.

Authors: Wataru Ono, Daiki Oka, Tomohiro Noguchi