Pressurized liquids vs. high intensity focused ultrasounds for the extraction of proteins from a pomegranate seed waste

Abstract

Pomegranate processing results in a waste with high protein content and potential industrial applicability. The reuse of these proteins requires their previous extraction and characterization. Nevertheless, extraction of proteins from vegetal tissues is a difficult task, and methodologies commonly applied for this purpose are non-sustainable and show low yields. Pressurized liquids extraction (PLE) is a sustainable technique scarcely applied for the extraction of proteins. PLE and high intensity focused ultrasounds (HIFU) have been compared in this work to recover proteins from a pomegranate seed waste. PLE extracted more proteins than HIFU, but it took longer and still co-extracted phenolic compounds. Extracted proteins were also characterized. Proteins separation by isoelectrofocusing electrophoresis revealed that the extraction technique, PLE or HIFU, significantly affected the solubility of proteins. Peptides released by simulated gastrointestinal digestion of extracted proteins also showed important differences when they were identified by UHPLC-MS/MS. Many identified peptides showed common features with antioxidant, antihypertensive, and hypocholesterolemic peptides. These activities were also confirmed by in vitro studies. PLE samples demonstrated, in general, higher bioactivity than HIFU. In addition to phenolic compounds, significantly co-extracted with proteins by PLE, other interesting compounds were also identified (e.g. azelaic acid). Extraction of proteins is usually carried out using non-sustainable methods that results in low yields and protein degradation. This work purposes the use of pressurized liquids extraction (PLE) for the recovery of proteins from a pomegranate seed waste, and compares these results with the obtained using high intensity focused ultrasounds (HIFU). PLE extracted more proteins but it required longer times than HIFU and co-extracted more phenolic compounds. The extraction procedure significantly affected proteins solubility and extracts composition. Proteins, peptides, and phenolic compounds contributed to the bioactivity of extracts. This work demonstrates that this waste is a sustainable and cheap source of proteins and bioactive molecules with high potential for the preparation of bioactive compounds, nutraceuticals, and cosmetics.

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