Genomic basis of the distinct biosynthesis of β-glucogallin, a biochemical marker for hydrolyzable tannin production, in three oak species

Hydrolyzable tannins (HTs), predominant polyphenols in oaks, are widely used in grape wine aging, feed additives, and human healthcare. However, the limited availability of a high-quality reference genome of oaks greatly hampered the recognition of the mechanism of HT biosynthesis. Here, high-quality reference genomes of three Asian oak species (Quercus variabilis, Quercus aliena, and Quercus dentata) that have different HT contents were generated. Multi-omics studies were carried out to identify key genes regulating HT biosynthesis. In vitro enzyme activity assay was also conducted. Dual-luciferase and yeast one-hybrid assays were used to reveal the transcriptional regulation. Our results revealed that β-glucogallin was a biochemical marker for HT production in the cupules of the three Asian oaks. UGT84A13 was confirmed as the key enzyme for β-glucogallin biosynthesis. The differential expression of UGT84A13, rather than enzyme activity, was the main reason for different β-glucogallin and HT accumulation. Notably, sequence variations in UGT84A13 promoters led to different trans-activating activities of WRKY32/59, explaining the different expression patterns of UGT84A13 among the three species. Our findings provide three high-quality new reference genomes for oak trees and give new insights into different transcriptional regulation for understanding β-glucogallin and HT biosynthesis in closely related oak species.

Effect of oil extraction on physicochemical and structural properties of starch isolated from acorn (Quercus brantii)

Acorn (Quercus brantii) is a rich source of starch. Since the presence of lipids affects the physicochemical properties of starch and the extraction of nutritious acorn oil and its starch is economical, it's essential to study the acorn starch characteristics before and after oil extraction. Firstly, the best condition for reaching the maximum extraction yield of acorn starch (AS) was determined, and defatted acorn starch (DAS) was extracted in the same conditions. Then the physicochemical properties of both samples were compared. The structural properties were investigated by Scanning Electron Microscopy images. The maximum yield of AS was obtained in a 1:10 ratio (acorn flour: water) at 45 °C and 180 min. Results demonstrated significant differences between color parameters and fat content (0.65 ± 0.04 and 12 ± 0.02) of AS and DAS. Also, DAS had higher swelling power, solubility, and lower turbidity than AS. The X-ray diffraction pattern showed that AS was C-type with relative crystallinity of 27.77 %. Pasting, thermal, and textural properties reflected the higher viscosity, gelatinization, retrogradation, and hardness for DAS compared to AS. Consequently, all of these analyses exhibited structural changes in acorn starch by removing lipids from acorn flour and provided essential information for further applications of acorn starch in different industries.

Traits variation of acorns and cupules during maturation process in Quercus variabilis and Quercus aliena

Quercus variabilis and Quercus aliena are two native tree species in China, which have similar habitats, and their regeneration mainly depends on acorn dispersal. This study analyzed the contents of water, soluble sugar, starch, soluble protein, and total phenolics in acorns and cupules during the whole development process to explore the difference between species. Thereinto, starch and total phenol occupied the dominant roles as their high contents. The acorn starch contents increased sharply during development in both species, but the contents in Q. variabilis were almost twice those of Q. aliena when mature. Similarly, high expression levels of starch synthase, soluble starch synthase 2 (SSS2) were also found in the acorns of Q. variabilis. The total phenol contents in Q. variabilis acorns were high at the early stages, and decreased sharply to similar contents in Q. aliena when mature. Additionally, the cupules in Q. variabilis had high contents of total phenols during the whole development period. Similar trends were also found in the expression patterns of UGT84A13 and SDH. The high total phenols in acorns and cupules of Q. variabilis probably protect the acorns from Mechoris ursulus, as only Q. aliena suffered a severe pest infestation in the early development stages. This study not only clarifies the interspecific difference between storage and defense substances during the development process in acorns and cupules, but also deepens understanding the specialized mechanisms of plant-pest/animal interactions in Quercus.

The effect of acorn muffin consumption on glycemic indices and lipid profile in type 2 diabetic patients: A randomized double-blind placebo-controlled clinical trial

Acorn is a nutritious fruit with the reported potential of ameliorating diseases, including diabetes. This research aimed to assess the effects of acorn muffin consumption on glycemic, lipid indices, and appetite in patients with type 2 diabetes. Sixty-six subjects were dichotomized to receive either one muffin containing 10 grams of acorn flour or a placebo muffin containing white wheat flour (no bran), per day, for 8 weeks. Acorn muffin consumption improved glycated hemoglobin (p = .06, mean difference [MD] = -0.65), triglyceride (p = .06, MD = -36.38), and high-density lipoprotein (p = .05, MD = 1.30), albeit only marginally significantly. Among appetite parameters, hunger, desire to eat, and prospective to eat were significantly lower, and satiety and fullness were significantly higher, in the acorn muffin group. In conclusion, acorn muffins could be utilized as an adjuvant therapy to control appetite and ameliorate glycated hemoglobin in patients with type 2 diabetes. However, further investigations are required for a more comprehensive conclusion.

Food Security beyond Cereals: A Cross-Geographical Comparative Study on Acorn Bread Heritage in the Mediterranean and the Middle East

This article aims to contribute to the limited literature on traditional gastronomic knowledge concerning acorn-based bread by ethnographically documenting the ingredients, preparation techniques and consumption practices of baked goods made from acorn seeds and flour that are still used today or at least still present in living memory. A qualitative comparative case method was adopted, and ethnographic data were gathered from 67 people in six selected Mediterranean, Central Asian and Middle Eastern countries. The analysis highlighted distinct trajectories in the development of acorn-based bread, showing some differences in terms of ingredients, preparation techniques and baking methods in the two cultural and geographical macro-regions. By exploring the evolution of the alimentary role of acorn bread in the past century, our findings also support the hypothesis that the product, at least during the last two centuries, has mostly been used as a famine food. By acknowledging the cultural importance of acorn fruits and acorn-based products, this study suggests that the rediscovery of acorn-based products and associated traditional knowledge may foster the sustainable development of rural and marginal regions in the Mediterranean, Middle East and Central Asia. This could help to reinforce the resilience of local communities and thus increase food security. Furthermore, reassessing acorns as a foodstuff may aid in developing innovative products in line with emerging trends in the food sector, which is looking for new non-cereal-based bakery products and other novel culinary applications.

Effects of pH and Ionic Salts on the Emulsifying and Rheological Properties of Acorn Protein Isolate

This study was designed to evaluate the emulsifying and rheological properties of acorn protein isolate (API) in different pH mediums (pH 3, 7 and 9) and in the presence of ionic salts (1 M NaCl and 1 M CaCl2). API shows higher solubility in distilled water at pH 7, while at the same pH, a decrease in solubility was observed for API in the presence of CaCl2 (61.30%). A lower emulsifying activity index (EAI), lower stability index (ESI), larger droplet sizes and slight flocculation were observed for API in the presence of salts at different pHs. Importantly, CaCl2 treated samples showed relevantly higher EAI (252.67 m2/g) and ESI (152.67 min) values at all pH as compared to NaCl (221.76 m2/g), (111.82 min), respectively. A significant increase in interfacial protein concentration (4.61 mg/m2) was observed for emulsion at pH 9 with CaCl2, while the major fractions of API were observed in an interfacial layer after SDS-PAGE analysis. All of the emulsion shows shear thinning behavior (τc > 0 and n < 1), while the highest viscosity was observed for emulsion prepared with CaCl2 at pH 3 (11.03 ± 1.62). In conclusion, API, in the presence of ionic salts at acidic, neutral and basic pH, can produce natural emulsions, which could be substitutes for synthetic surfactants for such formulations.

Structural and Physicochemical Properties of Tunisian Quercus suber L. Starches for Custard Formulation: A Comparative Study

The aim of the present study was to extract starch from acorn (Quercus suber L.) fruits using water and alkaline methods. Structural and functional properties of extracted starches were investigated and compared to those of corn and modified starches in order to determine their innovative potential application in food industry. The yield of extraction using the two methods was about 48.32% and 48.1%. The isolated starches showed low moisture, fat and protein contents, revealing high purity and quality. Additionally, the starch extracted using the alkaline method (AAS) showed higher lightness (60.41) when compared to starch isolated using hot water (WAS). However, the lightest white color was found for studied commercial starches. Moreover, AAS starch exhibited the highest swelling power, solubility and water absorption, followed by WAS and commercial starches. Results showed that extracted acorn starches were characterized by greater enthalpy and gelatinization temperatures. Similar observations were noted using FT-IR spectra analysis for all analyzed starches. In addition, granule starches observed using scanning electron microscopy were found to be spherical and ovoid. However, from the analysis by X-ray diffraction, a crystalline pattern of C-type was found for acorn starches, while commercial starches presented an A-type pattern. As an innovative food application, these underexploited acorn starches were valued and served to produce new custards with improved functional properties and better microstructure when compared to commercial custard.

Physicochemical, Structural, Thermal and Rheological Properties of Flour and Starch Isolated from Avocado Seeds of Landrace and Hass Cultivars

The objective of this study was to obtain and characterize flours and starches from the avocado seeds of Hass and landrace cultivars. The morphological, physical-chemical, structural, thermal and rheological characteristics were evaluated. The flour yield of the Hass and landrace cultivars was 41.56 to 46.86% (w/w), while for starch, it was 35.47 to 39.57% (w/w) (cv. Hass and landrace, respectively). Scanning electron microscopy (SEM) revealed the presence of oval starch granules and other particles in flour, in contrast to flours, starches showed lower ash, proteins and lipids content. However, the amylose content was higher in starches (42.25–48.2%). Flours showed a higher gelatinization temperature (T_p = 73.17–73.62 °C), and their starches presented greater gelatinization enthalpy (∆H_gel = 11.82–13.43 J/g). All samples showed a B-type diffraction pattern, and the crystallinity was higher in the flours. The rheological analysis (flow curves and viscoelastic tests) evidenced a pseudoplastic (n = 0.28–0.36) behavior in all samples analyzed, but the consistency index (k) was higher in starches. In general, the flours and starches from avocado seeds presented interesting proximal, thermal and functional properties for possible application in food systems, and these findings could contribute to the revaluation of this by-product.