Roles of Drying, Size Reduction, and Blanching in Sustainable Extraction of Phenolics from Olive Leaves

Abstract

It is now known that olive leaves contain a sizable portion of polyphenols and there is much research highlighting that these natural ingredients favorably exhibit bio-functional activities. In this regard, many studies have focused on the exploration of optimum conditions involved directly in the extraction process. These investigations, while being highly valuable, may somewhat cast a shadow over other contributing factors such as those involved in the preprocessing of leaves, including size reduction, drying, and blanching. The use of these unit operations under appropriate conditions, together with other benefits, potentially exert improved surface area, homogeneity, and diffusion/mass transfer which may help develop the liberation of target bio-compounds. The research work in this area, particularly size reduction, is relatively limited. Although in various experiments they are incorporated, not many studies have focused on them as the main predictor variables. The performance of further research may help ascertain the magnitude of their effects. Consideration of the operational parameters in preprocessing step is equally important as those in the processing/extraction step that may comparably influence on the extraction efficiency. This review provides an overview of the potential roles of drying, size reduction, and blanching in the extraction efficiency of phenolics from olive leaves.

Comparative study of different particle sizes of added olive leaves for the content of target polyphenols in virgin olive oil

“…19 The obtained results here, regardless of the factor of particle size, concur with previous research that observed significant effects of adding olive leaves on the increment of aforementioned pigments in the final extracted oil. 20…”

“…The choice of adding dry leaves rather than fresh ones was based on the extensive studies reviewed previously. 2,3…”

“…Total phenolic content (TPC). In general, regardless of the factor of particle size, previous studies justied the favorable effects of adding leaves on TPC enhancements 17,[20][21][22] , though there is no consensus on their ndings due to variations in percentages of added leaves, [23][24][25][26] processing designs, 27 harvesting times, 20 along with others.…”

Extraction Methods, Quantitative and Qualitative Phytochemical Screening of Medicinal Plants for Antimicrobial Textiles: A Review

“…The selection of pre-treatment and processing methods may influence the reduction in extraction time, an increase in extraction yield, quality of the biological compounds, and reduction in input energy [ 28 ]. The drying of any biomass inhibits microbial growth [ 18 ], and it aids in the longer shelf life and transportation costs due to the weight and space of dry products [ 29 , 30 , 31 ].…”

“…The drying of any biomass inhibits microbial growth [ 18 ], and it aids in the longer shelf life and transportation costs due to the weight and space of dry products [ 29 , 30 , 31 ]. Drying can affect the phytochemical components of the thermally sensitive components [ 29 , 32 , 33 , 34 ], and the process can also contribute to improved conservation of the bioactive compounds against oxidative [ 35 ] and enzymatic activities [ 36 ] and spoilage bacteria [ 30 , 37 , 38 ], enabling cellular destruction [ 28 , 30 , 35 ]. There are many different drying methods, e.g., thermal through natural convection (shade and open sun drying), forced convection (oven drying, solar drying, and heat pump drying), freeze-drying, greenhouse drying, microwave drying, and infrared drying [ 28 ].…”