Techno-functional and physicochemical properties of lentil flour with different particle sizes.

CARBONI, ANGELA DANIELA; MARTINS, GONÇALO NUNO; FERRERO, CRISTINA; PUPPO, MARIA CECILIA; CASTILHO, PAULA CRISTINA

Castelo Branco

Encuentro; XVI Encontro de Quimica dos Alimentos; 2022

Bread and cookies are amongst the most consumed foods worldwide. Wheat and corn flours are traditionally used as their main components, providing nutritional and functional value. Legume flours are being increasingly used in industries and at home because they improve the nutritional profile of foods and help tackle waste production of uncommercialized grains. The particle size distribution of a given flour determines some of its techno-functional characteristics and can modify the final quality of products in which they are applied. The objective of this study was to evaluate the particle size distribution of flour obtained from thermally treated lentil and the impact of granulometry in different techno-functional and physicochemical characteristics.Dry lentil (Lens culinaris Medikus var. variabilis) seeds (Don Elio, Argentina) were soaked in distilled water for 8 h (ca. 25 °C) and then were cooked in a fresh batch of water for 30 min at boiling temperature. Afterwards, the lentils were dried in a dehydrator (12 h - 60 °C), and ground using an electric domestic grinder. Lentil flour was fractionated using a set of sieves obtaining 5 fractions (F). Their particle sizes were in the following ranges, in mm: F1 ≥ 1.0; 1.0 > F2 ≥ 0.50; 0.50 > F3 ≥ 0.250; 0.250 > F4 ≥ 0.125; 0.125 > F5. The fractions’ moisture content was evaluated by a moisture analyser, while the AACC 08-01 method1 was used to assess ash contents. Also, the flours’ Water Holding Capacity (WHC) and Oil Holding Capacity (OHC) were also evaluated. Fourier Transform Infrared spectroscopy with Attenuated Total Reflectance (ATR-FTIR) was used to evaluate the presence of macrocomponents. Besides, samples were observed using Scanning Electron Microscopy (SEM) in order to study the microstructure of the different fractions. Unfractionated flour (UF) was also submitted to all the previous analysis.After fractionating, particle size distribution was: 17.8, 28.7, 17.8, 9.6, 26.1 %, from F1 to F5, meaning the major constituents of treated lentil’s flour have between 1.0 and 0.250 mm of diameter. The obtained fractions were clearly physically different in terms of color and general appearance. F1 has a heterogenic aspect with particles of various shapes and light to dark tones, which turn to completely homogenous light-brownish particles in F5. Finer flours showed higher moisture contents with values going from 4.6 % in F1 to 7.6 % in F5, probably due to their greater surface areas. Ash content ranged between 1.2 and 2.0 %, observing the lowest content in F5, which can be related to the loss of the outer layers of the seed during grinding. Results of WHC were higher in the coarser fractions. OHC results were inconsistent with particle size, with F5 presenting the lowest value obtained. These differences may be due to the greater or lesser presence of lipophilic components in the different fractions. The ATR-FTIR analysis showed peaks related to carbohydrates, lipids, and protein in all spectra, with no noteworthy differences among the various samples. SEM images showed F1 is composed of F5 particles that with grinding detach from the main structure. F3 was shown to be an intermediate state, with the coarser and finer structures coexisting.Thermally-treated lentil’s flour is mainly composed of fractions with high granulometry. This is advantageous for preparing foods that require low enzymatic digestion. High WHC values are desirable when improving properties in baked goods, like their specific volume, while samples with high OHC values are useful for enhancing palatability and flavor retention. In this sense, F3 could be considered the best fraction, balancing functional properties with general aspect and an intermediate particle size. Overall, granulometry affected the physicochemical and techno-functional properties of the thermally-treated lentil’s flour. The differences found between fractions would allow their use for the preparation of different foods according to different needs.