Spray-drying microencapsulation of synergistic antioxidant mushroom extracts and their use as functional food ingredients

Highlights

• S. luteus and C. atramentaria extract gave synergistic antioxidant effects.

• The extract incorporation in cottage cheese increased its initial antioxidant activity.

• The microencapsulated extract preserved more the cottage cheese antioxidant activity.

• Nutritional properties and colour were kept in the cottage cheeses with the extracts.

Abstract

In this work, hydroalcoholic extracts of two mushrooms species, Suillus luteus (L.: Fries) (Sl) and Coprinopsis atramentaria (Bull.) (Ca), were studied for their synergistic antioxidant effect and their viability as functional food ingredients tested by incorporation into a food matrix (cottage cheese). In a first step, the individual extracts and a combination of both, showing synergistic effects (Sl:Ca, 1:1), were microencapsulated by spray-drying using maltodextrin as the encapsulating material. The incorporation of free extracts resulted in products with a higher initial antioxidant activity (t0) but declining after 7 days (t7), which was associated with their degradation. However, the cottage cheese enriched with the microencapsulated extracts, that have revealed a lower activity at the initial time, showed an increase at t7. This improvement can be explained by an effective protection provided by the microspheres together with a sustained release. Analyses performed on the studied cottage cheese samples showed the maintenance of the nutritional properties and no colour modifications were noticed.

Introduction

Mushrooms are widely appreciated all over the world for their nutritional properties (Kalač, 2009). They have a low fat content but are rich in water, minerals, proteins, fibres and carbohydrates (Heleno et al., 2012, Kalač, 2009, Reis et al., 2012, Reis et al., 2011). Besides their nutritional value, it has been demonstrated that mushrooms have health promoting benefits (Palacios et al., 2011). They are effective as anti-inflammatory (Ma, Chen, Dong, & Lu, 2013), antitumor (Heleno et al., 2014), antibacterial (Alves et al., 2012) and antioxidant agents (Reis et al., 2011), extending their potential use as functional foods and applications in the biomedical field.

During natural cellular metabolism, reactive oxygen (ROS), nitrogen (RNS) and sulphur (RSS) species are produced (Carocho & Ferreira, 2013), ROS being the most abundant (Ferreira, Barros, & Abreu, 2009). When high concentrations of these species are present, an oxidative stress is generated. If in excess, ROS may oxidise and damage cellular lipids, proteins and DNA, leading to their modification and inhibition of normal functions (Ferreira et al., 2009). Given this scenario, the organism develops defence mechanisms such as endogenous defences, including enzymatic reactions such as the production of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px) and glutathione reductase; or non-enzymatic reactions, resulting in species such as glutathione (GSH), α-tocopherol (vitamin E), ascorbic acid (vitamin C) and lipoic acid (Carocho and Ferreira, 2013, Ferreira et al., 2009). Both mechanisms are able to provide cells protection against excessive levels of free radicals (Carocho & Ferreira, 2013).

The exogenous antioxidant defence promoters can be ingested as part of the daily diet to help fight against high ROS contents. Therefore, mushrooms can play an important role since they contain diverse phenolic compounds, known to be excellent antioxidants due to their capacity for capturing free radicals by electron transferring, and to the excellent redox properties of the phenolic hydroxyls groups (Ferreira et al., 2009).

Apart from their instability at high temperatures, and in the presence of oxygen and light, some mushroom extracts are characterised by a strong odour and flavour. One way to ensure their viability as functional food ingredients is to proceed with their microencapsulation, providing protection against oxidation and masking their odour and flavour (Ersus and Yurdagel, 2007, Fang and Bhandari, 2010). Despite the numerous available microencapsulation possibilities, spray-drying is still one of the most widely used processes to encapsulate food ingredients (Fang & Bhandari, 2010). Among the main advantages of this technique are its easy industrialisation and the possibility of continuous production. Nevertheless, prolonged contact with high temperatures can compromise the bioactive properties of the mushroom extracts, and should be avoided.

Among several possibilities, maltodextrin (MD), a hydrolysed starch, offers advantages as a microencapsulation material (Gharsallaoui, Roudaut, Chambin, Voilley, & Saurel, 2007). It is a low cost material with a neutral aroma and flavour, high water solubility and low viscosity at high solids content, being able to provide effective protection against oxidation (Ersus and Yurdagel, 2007, Saéns et al., 2009).

Microencapsulation can be applied to protect bioactive natural extracts and some examples calling up this thematic can be found in literature (Dias, Ferreira, & Barreiro, 2015). Nevertheless, these studies are mainly related to the development of the microencapsulation process and do not proceed with the implementation of a final application as a functional food. (Ersus and Yurdagel, 2007, Kha et al., 2010, Saéns et al., 2009, Silva et al., 2013, Wu et al., 2014). In fact, and according to the current research, the examples dealing with the full process development are scarcer. In this context, Çam, Içyer, and Erdoğna (2014) tested the incorporation of microencapsulated Punica granatum L., an extract from pomegranate, in ice creams, and Martins et al. (2014) studied the incorporation of Rubus ulmifolius Schoot (Rosaceae), a species of wild blackberry, microencapsulated in alginate microparticles in yogurt. The obtained results, rather preliminary, are encouraging interest in the development of foods enriched with natural extracts that are often referred as health promoters (Ramalingum & Mahomoodally, 2014).

In this work, extracts of two mushroom species, Suillus luteus (L.: Fries) and Cooprinopsis atramentaria (Bull.) were investigated for their synergistic antioxidant effects and a promising combination of both (in similar proportions) was chosen to be microencapsulated by spray-drying using maltodextrin as the encapsulating material. The obtained powders were characterised by Scanning Electron Microscopy (SEM) (to inspect morphology and particle size) and for their antioxidant activity (free radicals scavenging activity and reducing power). Encapsulation yield and efficiency were also estimated. As a final step in this work, the produced microspheres were incorporated into cottage cheese samples and their antioxidant activity, nutritional value and colour were determined and compared with the counterparts, using extracts in the free form and a control (sample with no added extracts).