Kinetic study on the effects of sugar addition on the thermal degradation of phycocyanin from Spirulina sp.

Abstract

Phycocyanin is a source of antioxidants and natural colorants extracted from microalgae. It undergoes color, concentration, and antioxidant activity degradations during heating processes, such as in food processing. The effects of different kinds of sugars as stabilizer and elevation of temperature were studied. Glucose, sucrose, or fructose as stabilizer were mixed in phycocyanin solution, which was heated to 40 °C, 60 °C, and 80 °C for 60 min. Results showed that phycocyanin degraded significantly without any sugar addition. The addition of glucose could increase the activation energy by up to fourfold due to the polymerization of protein phycocyanin by sugar, and glucose could prevent damage of the phycocyanin structure. Phycocyanin underwent discoloration from bright blue to faint blue after heating at 80 °C. Fructose addition in phycocyanin could minimize color degradation at 80 °C, whereas glucose addition could increase the antioxidant activity of phycocyanin by decreasing IC₅₀ up to 18.47%.

Introduction

Food colorants are widely used as an additive material in both manufacturing and consumer food industries due to their compatibility with food processes (Yamjala, Nainar, & Ramisetti, 2016). Natural food colorants from natural sources, such as plants or fruits, have been used since 1500 BCE, but they were replaced by synthetic colorants in the early 19th century because of the industrial revolution (Downham & Collins, 2000). Natural colorants currently dominate 31% of the dye market, whereas 40% are synthetic colorants (Mapari, Thrane, & Meyer, 2010). The rising market in natural colorants is caused by awareness of diet and health, which starts with the reduced consumption of synthetic material.

Several plants and fruits are currently used as natural colorants, such as Rosella (red), grape (purple), carrots (orange), blueberry (blue), or Pandanus leaves (green) (Duangmal, Saicheua, & Sueeprasan, 2008; Clydesdale, Francis, & Damon, 1978; Kirca, Ǒzkan & Cemeroğlu, 2007; Fracassetti et al., 2013; Ningrum, Minh, & Schreiner, 2015). However, the utilization of microalgae extract as a natural colorant is also increasing, particularly phycocyanin (blue) from Spirulina sp., β-carotene (orange) from Dunaliella sp., or astaxanthin (red) from Haematococcus sp. (Dufossé et al., 2005). Most food colorants are also used as antioxidants to reduce free radicals.

Phycocyanin is a natural colorant extracted from microalgae. This pigment–protein complex compound can be extracted from blue-green algae (cyanobacteria) Spirulina sp., and it is classified as a phycobiliprotein (Markou & Nerantzis, 2013). The molecular weight, position, and maximum absorption intensity of phycocyanin depend on the state of aggregation, which is affected by pH solution, temperature, protein concentration, and origin of the algae itself (Mishra, Shrivastav, & Mishra, 2008). Phycoyanin captures oxygen radicals because it contains an open tetraphyrrole chain that can bind a peroxy radical by donating hydrogen atoms, which are bonded in the 10th C atom from a tetraphyrrole molecule (Estrada et al., 2001, Romay et al., 2003).

In its application as a natural food colorant, degradation of color, concentration, and antioxidant activity often occurs due to high temperatures during food processing. Phycocyanin gradually changes from light blue to faint blue, and this transformation is a disadvantage in the food industry because of the resulting unattractive hue. Several techniques have been used to prevent the thermal degradation of phycocyanin, such as the addition of a stabilizer (Antelo et al., 2008, Sun et al., 2006), pH adjustment (Wu, Wang, Xiang, Li, & He, 2016), and encapsulation (Chen et al., 1996).

Stabilizer addition is commonly used to minimize the thermal degradation of phycocyanin due to its simplicity and economy. Sugar is a stabilizer that is typically used to stabilize proteins that are easily degraded, and it has a simple structure such as monosaccharide (glucose, fructose, and galactose) or disaccharide (maltose, lactose, and sucrose). Sugar can bind with protein via an N-linked glycosidic bond, which can minimize thermal degradation during food processing (Allison et al., 1999, Imamura et al., 2003). The utilization of sugar as a stabilizer in the food industry has been studied by Martelli, Folli, Visai, Daglia, and Ferrari (2014), who used sugar to reduce the anthocyanin degradation of raspberry. Meanwhile, Vikram, Ramesh, and Prapulla (2005) used sugar to reduce the nutrient degradation of orange juice. In another experiment, Sadilova, Stintzing, Kammerer, and Carle (2009) attempted to add sugar to fruit juices to stabilize the anthocyanin content. Therefore, sugar is a promising stabilizer that can be used to prevent the thermal degradation of phycocyanin.

In the present study, commercial sugar with simple structures (i.e., glucose, fructose, and sucrose) was used as a promising phycocyanin stabilizer to minimize thermal degradation. The reaction kinetics of the thermal degradation of phycocyanin and the activation energy were studied. Phycocyanin color changes were also observed before and after heating using a colorimeter. Enhanced antioxidant activity after heating will be helpful to establish a baseline protocol for antioxidant stability.