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Walnut kernels, selected as the raw material, underwent hydrolysis with protein-glutaminase (PG) following pulping. This process laid the foundation for producing set-type walnut yogurt, involving steps such as blending, homogenization, sterilization, and fermentation. The study investigated the impact of protein-glutaminase and five distinct starter cultures labeled I~V on the quality of walnut yogurt. This was evaluated by examining the yogurt's fermentation characteristics, physicochemical indicators, and microstructure. Furthermore, walnut yogurt developed under these optimal conditions was compared to traditional milk yogurt to assess its quality and characteristics. The findings revealed a significant improvement in the fermentation characteristics and textural parameters of yogurt fermented by walnut milk following enzymatic hydrolysis compared to non-enzymatic walnut milk. The optimal conditions were identified as 0.2% enzyme concentration and a 40-minute reaction time, with the pH, acidity, hardness, and consistency of walnut yogurt being 4.3, 55°T, 85.30 g, and 583.96 g·s, respectively. Walnut yogurt developed using starter culture I exhibited the highest acidity level, maintaining minimal fluctuation over a 21-day storage period. In contrast, yogurts prepared with alternative starter cultures demonstrated varying degrees of stratification and sedimentation. The yogurt fermented with culture I showed superior viscoelastic properties, presenting a denser gel network. Conversely, yogurts fermented with cultures IV and V displayed reduced apparent viscosity, lower values of G' (storage modulus), and G'' (loss modulus), along with a looser gel structure. Additionally, walnut yogurt produced with starter culture I maintained bacterial counts exceeding 106 CFU/mL throughout the storage duration. Despite walnut yogurt requiring further refinement in aspects such as consistency, water-holding capacity, and whey release rate compared to milk yogurt, the overall impact of PG was positive, enhancing the gelation quality of walnut yogurt. The yogurt prepared with starter culture I (Lactobacillus bulgaricus and Streptococcus thermophilus) was notably improved, receiving favorable overall assessments.

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Copyright of Current Biotechnology (2095-2341) is the property of Chinese Academy of Agricultural Sciences, Institute of Biotechnology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The effect of roasting and high-pressure homogenization on the quality of yogurt made from peeled walnut kernels was explored in this study. The G' and G'' values of yogurt made from walnuts roasted at high temperatures were reduced. The water-holding capacity and hardness of walnut yogurt were reduced to 47.73% and 24.22 g, respectively. Increasing the homogenization pressure reduced the particle size of the walnut yogurt to 20.50 μm. Homogenized walnut milk at 150 MPa increased the viscosity, hardness, and consistency of yogurt product from 11.71 to 16.74 Pa.s, from 30.01 to 71.63 g and from 283.17 to 455.24 g·s, respectively. The confocal laser scanning microscope observation demonstrated a reduction in the size of fat and protein micelles in the homogenized yogurt samples, resulting in a compact structure. This study will contribute valuable scientific insights to the advancement of plant-based yogurt quality.

This study aims to investigate better alternatives to animal milk sources for yogurt production. Walnut yogurt was produced by fermentation with Lactiplantibacillus plantarum , a member of the genus Lactobacillus. Its nutritional value and physicochemical properties were analyzed and compared with those of animal yogurts. The results showed that: compared to walnut milk, fermentation resulted in an increase in the content of organic acids (2260.00 mg/kg), total phenolic content (19.23 μg/ml) and DPPH free radical scavenging activity (94.61%) of walnut yogurt. In addition, the content of bitter amino acids in walnut yogurt was reduced by 92% and the flavor quality and antioxidant activity were improved. The content of protein (5.67 g/100g), fat (54.85 g/100g), total solids (19.40 g/100g), total free amino acids (441.39 μg/mL) and bioactivity of walnut yogurt were higher than those of commercially available animal yogurt. Walnut yogurt was found to be acceptable by sensory evaluation. Overall, walnut yogurt had different physicochemical properties (such as total solids content) and higher nutritional value (including antioxidant activity) compared to animal yogurt. This study highlights the differences and advantages between plant-based yogurt and animal-based yogurt, and provides a scientific basis for further optimizing the formula and production process of plant-based yogurt. • Properties of pure walnut yoghurt and animal yoghurt are compared for the first time. • Lactiplantibacillus plantarum fermented walnut milk reduces bitter amino acids. • Fermentation with Lactobacillus enhances the nutritional values of walnut yogurt. • Walnut yogurt has the highest antioxidant activity and free amino acid content. [ABSTRACT FROM AUTHOR]

Copyright of Shipin Kexue/ Food Science is the property of Food Science Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)