The use of OH, with the associated non-thermal effects due to the presence of an electrical field and frequency, has been suggested for protein functionalization, microbial inactivation and extraction of compounds from biological matrices. Among the latter, microalgae are considered nowadays as a very valuable source of compounds of interest for the energy sector, pharma, and food and the individuation and selection of the proper extraction technique to recover these compounds is very challenging due to the intrinsic nature of the microalgae cell walls, which limits the mass transfer through it. A very interesting study case is represented by Chlorella vulgaris, a microalga which is able to accumulates considerable amounts of pigments such as carotenoids and chlorophyll a and b, as well as other organic compounds such as lipids, carbohydrates and proteins, which can be used to enhance the nutritional content of conventional food and, hence, to positively affect humans health. The main objective of this study is to investigate the electrical effects of OH on the extraction of pigmented solutes from C. vulgaris. OH treatments of C. vulgaris cultures - with a concentration of 0.33 g/L and adjusted electrical conductivity of 1 mS/cm – were carried out by applying alternating sinusoidal waves of 25 kHz and electric fields of up to 50 V/cm. The operating temperatures range was from 22 ºC up to a maximum of 45 ºC. The extracted pigments were characterized utilizing spectrophotometric and spectrofluorometric methods. The results showed that extraction yield of total pigments in the OH assisted process was 15 times higher with respect to that of a conventional extraction process, being the concentration of chlorophyll a, b and carotenoids in the aqueous medium equal to 0.64±0.04 μg/mL, 0.49±0.01 μg/mL and 0.48±0.05 μg/mL, respectively. Indeed, the the concentration of of chlorophyll a, b and carotenoids in the aqueous medium in the extracts obtained with the conventional process was 0.13±0.02 μg/mL 0.3±0.04 μg/mL, chlorophyll b and 0.14±0.01 μg/mL, respectively. In conclusion, OH has the potential to improve extraction of pigmented solutes from a non-concentrated biomass of C. vulgaris at mild temperatures (below 50 ºC) and low alternating electric fields. Further studies are necessary for a better understanding of the mechanisms involved in the OH assisted extraction process (e.g. effects of using different electrical frequencies and types of electrical wave). However, the demonstration of the positive effects of OH on the extraction of nutrients is particularly significant due to its potential use in the market of healthy foods, under the operational parameters tested – i.e. low electric fields, high frequency and low cell concentration – that favor energy efficiency and process reliability.
Enhancing extraction of food-grade pigments from the microalgae Chlorella vulgaris through application of Ohmic Heating
FRACCOLA, GIANLUCA;Pataro, G.;Ferrari, G.;
2016-01-01
Abstract
The use of OH, with the associated non-thermal effects due to the presence of an electrical field and frequency, has been suggested for protein functionalization, microbial inactivation and extraction of compounds from biological matrices. Among the latter, microalgae are considered nowadays as a very valuable source of compounds of interest for the energy sector, pharma, and food and the individuation and selection of the proper extraction technique to recover these compounds is very challenging due to the intrinsic nature of the microalgae cell walls, which limits the mass transfer through it. A very interesting study case is represented by Chlorella vulgaris, a microalga which is able to accumulates considerable amounts of pigments such as carotenoids and chlorophyll a and b, as well as other organic compounds such as lipids, carbohydrates and proteins, which can be used to enhance the nutritional content of conventional food and, hence, to positively affect humans health. The main objective of this study is to investigate the electrical effects of OH on the extraction of pigmented solutes from C. vulgaris. OH treatments of C. vulgaris cultures - with a concentration of 0.33 g/L and adjusted electrical conductivity of 1 mS/cm – were carried out by applying alternating sinusoidal waves of 25 kHz and electric fields of up to 50 V/cm. The operating temperatures range was from 22 ºC up to a maximum of 45 ºC. The extracted pigments were characterized utilizing spectrophotometric and spectrofluorometric methods. The results showed that extraction yield of total pigments in the OH assisted process was 15 times higher with respect to that of a conventional extraction process, being the concentration of chlorophyll a, b and carotenoids in the aqueous medium equal to 0.64±0.04 μg/mL, 0.49±0.01 μg/mL and 0.48±0.05 μg/mL, respectively. Indeed, the the concentration of of chlorophyll a, b and carotenoids in the aqueous medium in the extracts obtained with the conventional process was 0.13±0.02 μg/mL 0.3±0.04 μg/mL, chlorophyll b and 0.14±0.01 μg/mL, respectively. In conclusion, OH has the potential to improve extraction of pigmented solutes from a non-concentrated biomass of C. vulgaris at mild temperatures (below 50 ºC) and low alternating electric fields. Further studies are necessary for a better understanding of the mechanisms involved in the OH assisted extraction process (e.g. effects of using different electrical frequencies and types of electrical wave). However, the demonstration of the positive effects of OH on the extraction of nutrients is particularly significant due to its potential use in the market of healthy foods, under the operational parameters tested – i.e. low electric fields, high frequency and low cell concentration – that favor energy efficiency and process reliability.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
