In vitro DIAAS of Swiss soybean cultivars using the INFOGEST model: Increase in protein quality from soybean to soymilk and tofu.

To support the transition towards more sustainable and healthy diets, viable alternatives to foods of animal origin need to be identified. Many plant-based protein sources are currently marketed with claims of minimal environmental impact, but very limited consideration has been given to their protein quality and bioavailable mineral content considering the fact that animal-based foods are typically the primary source of both in Western diets. In this study, traditionally consumed soy foods (cooked soybeans, soymilk, tofu) from different Swiss soybean cultivars were nutritionally characterized and the in vitro digestibility of individual amino acids and total protein were assessed using an in vitro model based on the static INFOGEST protocol; the protein quality was evaluated using the in vitro digestible indispensable amino acid score (DIAAS). The results reveal an increase in total protein in vitro digestibility across the traditional soy food production value chain: 52.1-62.7% for cooked soybeans, 84.1-90.6% for soymilk, and 94.9-98.4% for tofu. Protein quality, determined using the recommended amino acid pattern for 0.5-3 years old, was "low" (no claim) for cooked soybeans (DIAAS < 60), while soymilk (DIAAS = 78-88) and tofu products (DIAAS = 79-91) were of similar "good" protein quality, with considerably higher DIAAS values than those of cooked soybeans (P < 0.001). The iron and zinc contents in soy foods were substantial, but high molar ratios of phytic acid (PA) to iron (PA/Fe; >8) and PA to zinc (PA/Zn; >15) indicate a possible strong inhibition of iron and zinc bioavailability. Based on the DIAAS results, soymilk and tofu would be suitable plant-based alternatives to animal-based foods, while future efforts should focus on optimizing soybean preparation to overcome the negative effects of the plant tissue matrix as well as processing steps to reduce mineral absorption inhibiting substances.

Mealworm larvae (Tenebrio molitor) and crickets (Acheta domesticus) show high total protein in vitro digestibility and can provide good-to-excellent protein quality as determined by in vitro DIAAS.

Edible insects, such as mealworms (Tenebrio molitor larvae; TM) and crickets (Acheta domesticus; AD), are a sustainable, protein-dense novel food with a favorable amino acid profile, which might be an alternative to animal proteins. To assess the protein quality of TM and AD, we assessed the digestible indispensable amino acid scores (DIAAS), considering individual amino acids and their ileal amino acid digestibility, using an in vitro model based on the INFOGEST digestion protocol. In addition, we evaluated if various processing and food preparation steps influenced the in vitro digestibility of individual amino acids and the in vitro DIAAS values of TM and AD and compared them to chicken breast as a reference of excellent protein quality. The total protein in vitro digestibility ranged from 91 to 99% for TM and from 79 to 93% for AD and was negatively affected by oven-drying and, to a lesser extent, by chitin-reduction. The in vitro DIAAS values were 113, 89, and 92 for chicken, blanched TM, and blanched AD, respectively, when considering the indispensable amino acid (IAA) requirements of young children between 6 months and 3 years. Across different processing and food preparation methods, the in vitro DIAAS values ranged between 59 and 89 for TM and between 40 and 92 for AD, with the lowest values found in chitin-reduced insects. Due to their similarities to chicken regarding protein composition, total protein in vitro digestibility, and in vitro DIAAS values, TM and AD might be an alternative to traditional animal proteins, provided that suitable processing and food preparation methods are applied. Our in vitro DIAAS results suggest that TM and AD can thus be considered good-quality protein sources for children older than 6 months. The DIAAS calculations are currently based on crude protein (total nitrogen × 6.25), resulting in an overestimation of insect protein content, and leading to an underestimation and potential misclassification of protein quality. The in vitro model applied in this study is a valuable tool for product development to optimize the protein quality of edible insects. Further studies are required to assess the in vivo DIAAS of insects in humans.