Color and structural modifications of alkaline extracted sunflower protein concentrates and isolates using L-cysteine and glutathione

Protein-phenolic interactions and reactions: Discrepancies, challenges, and opportunities

Although noncovalent interactions and covalent reactions between phenolic compounds and proteins have been investigated across diverse scientific disciplines, a comprehensive understanding and identification of their products remain elusive. This review will initially outline the chemical framework and, subsequently, delve into unresolved or debated chemical and functional food-related implications, as well as forthcoming challenges in this topic. The primary objective is to elucidate the multiple aspects of protein-phenolic interactions and reactions, along with the underlying overwhelming dynamics and possibilities of follow-up reactions and potential crosslinking between proteins and phenolic compounds. The resulting products are challenging to identify and characterize analytically, as interactions and reactions occur concurrently, mutually influencing each other. Moreover, they are being modulated by various conditions such as the reaction parameters and, obviously, the chemical structure. Additionally, this review delineates the resulting discrepancies and challenges of properties and attributes such as color, taste, foaming, emulsion and gel formation, as well as effects on protein digestibility and allergenicity. Ultimately, this review is an opinion paper of a group of experts, dealing with these challenges for quite a while and aiming at equipping researchers with a critical and systematic approach to address current research gaps concerning protein-phenolic interactions and reactions.

Hydrolysis of chlorogenic acid in sunflower flour increases consumer acceptability of sunflower flour cookies by improving cookie color

Sunflower meal, a byproduct of sunflower oil pressing, is not commonly used in alkaline baking applications. This is because chlorogenic acid, the main phenolic antioxidant in sunflower seeds, reacts with protein, giving the baked product a green discoloration. Our group previously demonstrated that a chlorogenic acid esterase from Lactobacillus helveticus hydrolyzes chlorogenic acid in sunflower dough cookie formulations, resulting in cookies that were brown instead of green. This study presents a sensory analysis to determine the acceptability of enzymatically upcycled sunflower meal as an alternative protein source for those allergic to meals from legumes or tree nuts. We hypothesized that the mechanism of esterase-catalyzed chlorogenic acid breakdown does not influence the cookies' sensory properties other than color and that consumers would prefer treated, brown cookies over non-treated cookies. Cookies made from sunflower meal were presented under green lights to mask color and tested by 153 panelists. As expected, the sensory properties (flavor, smell, texture, and overall acceptability) of the treated and non-treated cookies were not statistically different. These results corroborate proximate analysis, which demonstrated that there was no difference between enzymatically treated and non-treated cookies other than color and chlorogenic acid content. After the cookie color was revealed, panelists strongly preferred the treated cookies with 58% indicating that they "probably" or "definitely" would purchase the brown cookies, whereas only 5.9% would buy green, non-treated cookies. These data suggest that esterase-catalyzed breakdown of chlorogenic acid represents an effective strategy to upcycle sunflower meal for baking applications. PRACTICAL APPLICATION: Sunflower meal is currently used as animal fodder or discarded. A major factor preventing sunflower meal use is its high chlorogenic acid content, which causes a green discoloration of baked goods made from sunflower meals under alkaline conditions. This study presents a sensory analysis in which panelists evaluate cookies made with sunflower flour that was treated with an esterase that breaks down chlorogenic acid. The results show that enzymatic treatment prevents greening and that panelists strongly prefer esterase-treated, non-green cookies, thus demonstrating the feasibility of utilizing sunflower flour in baking applications.

Identification of alkaline-induced thiolyl-chlorogenic acid conjugates with cysteine and glutathione

Alkaline reactions of chlorogenic acid (CGA) yield undesirable development of brown or green pigments, limiting the utilization of alkalized CGA-rich foods. Thiols such as cysteine and glutathione mitigate pigment formation through several mechanisms, including redox coupling to reduce CGA quinones, and thiol conjugation, which forms colorless thiolyl-CGA compounds that do not readily participate in color-generating reactions. This work provided evidence of the formation of both aromatic and benzylic thiolyl-CGA conjugate species formed with cysteine and glutathione under alkaline conditions in addition to hydroxylated conjugate species hypothesized to arise from reactions with hydroxyl radicals. Formation of these conjugates proceeds more quickly than CGA dimerization and amine addition reactions mitigating pigment development. Differentiation between aromatic and benzylic conjugates is enabled by characteristic fragmentation of CS bonds. Acyl migration and hydrolysis of the quinic acid moiety of thiolyl-CGA conjugates yielded a variety of isomeric species also identified through untargeted LC-MS methods.

A review of the structure, function, and application of plant-based protein-phenolic conjugates and complexes

Interactions between plant-based proteins (PP) and phenolic compounds (PC) occur naturally in many food products. Recently, special attention has been paid to the fabrication of PP-PC conjugates or complexes in model systems with a focus on their effects on their structure, functionality, and health benefits. Conjugates are held together by covalent bonds, whereas complexes are held together by noncovalent ones. This review highlights the nature of protein-phenolic interactions involving PP. The interactions of these PC with the PP in model systems are discussed, as well as their impact on the structural, functional, and health-promoting properties of PP. The PP in conjugates and complexes tend to be more unfolded than in their native state, which often improves their functional attributes. PP-PC conjugates and complexes often exhibit improved in vitro digestibility, antioxidant activity, and potential allergy-reducing activities. Consequently, they may be used as antioxidant emulsifiers, edible film additives, nanoparticles, and hydrogels in the food industry. However, studies focusing on the application of PP-PC conjugates and complexes in real foods are still scarce. Further research is therefore required to determine the structure-function relationships of PP-PC conjugates and complexes that may influence their application as functional ingredients in the food industry.

Effect of de-phenolization on protein-phenolic interactions of sunflower protein isolate

Proteins and phenolic compounds are significant components of foods that can interact, and this interaction can impact the functional properties of proteins and the bioactivity of phenolic compounds. Sunflower meal, which has a high potential to be an important alternative protein source, contains phenolic compounds mostly bonded with proteins. In this study, the interaction between proteins and phenolic compounds which naturally exist in sunflower and prone to oxidation during alkaline treatment (for protein isolation) was investigated. There was a significant decrease up to 96.21% in the content of total phenolics by methanol washing. Chlorogenic acid, cryptochlorogenic acid and caffeic acid were detected in the phenolic extract obtained from sunflower protein isolate, and they exhibited different levels of reduction after methanol washing. For the total antioxidant capacity analysis, a decrease by 50% was observed after 4hwashing with methanol solution, and there was no significant decrease afterwards. In addition, the fluorescence intensity of sunflower protein was diminished with reduced washing time, which was mostly attributed to the protein-phenolic interaction. According to hydrodynamic parameters, the main force of the sunflower protein-phenolic complex formation was assumed to be hydrophobic attraction. The Stern-Volmer plot indicated that the main quenching mechanism was only static at all temperature conditions.

A highly active esterase from Lactobacillus helveticus hydrolyzes chlorogenic acid in sunflower meal to prevent chlorogenic acid induced greening in sunflower protein isolates

Chlorogenic acid (CGA) is an ester between caffeic and quinic acid. It is found in many foods and reacts with free amino groups in proteins at alkaline pH, leading to the formation of an undesirable green pigment in sunflower seed-derived ingredients. This paper presents the biochemical characterization and application of a highly active chlorogenic acid esterase from Lactobacillus helveticus. The enzyme is one of the most active CGA esterases known to date with a Km of 0.090 mM and a kcat of 82.1 s-1. The CGA esterase is easily expressed recombinantly in E. coli in large yields and is stable over a wide range of pH and temperatures. We characterized CGA esterase's kinetic properties in sunflower meal and demonstrated that the enzyme completely hydrolyzes CGA in the meal. Finally, we showed that CGA esterase treatment of sunflower seed meal enables the production of pale brown sunflower protein isolates using alkaline extraction. This work will allow for more widespread use of sunflower-derived products in applications where neutrally-colored food products are desired.