Optimisation of microencapsulation of turmeric extract for masking flavour

Highlights

• We solve the turmeric problems by masking its pungent flavour for food products.

• Brown rice flour and β-cyclodextrin were developed as a novel encapsulating agent.

• The optimal conditions were 5% of turmeric extract with 20 g/L of β-cyclodextrin.

• The turmeric powder with odour binding could be used as a functional food ingredient.

Abstract

The aim of this study was to evaluate the odour masking property, encapsulation efficiency and physicochemical properties of turmeric extract prepared by a binary blend of wall materials, i.e. brown rice flour (BRF) and beta-cyclodextrin (β-CD). Response surface methodology was applied to investigate the effect of encapsulation processing variables, including core loading mass (5–25%) and β-CD (5–20%) concentration on product recovery, moisture content, hygroscopicity, curcuminoids encapsulation and volatile release. To investigate odour masking properties of a wall material combination, volatiles in headspace were monitored by GC–MS using ar-turmerone and 2-methyl-4-vinylguaiacol as marker compounds to represent turmeric extract. The obtained results revealed an optimal encapsulation process was 5% of core loading mass with addition 20 g/L of β-CD, since it enabled high curcuminoids encapsulation with low volatile release, moisture content and hygroscopicity. Turmeric powder with reduced odour can be used as a nutrient supplement or natural colorant for food products.

Introduction

Turmeric extract consists of curcuminoids, a heavy fraction of yellowish brown colour. The compounds responsible for the yellow colour are curcumin (C; 1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadien-3,5-dione) and two curcuminoids, demethoxycurcumin (DMC) and bis-demethoxycurcumin (BDMC) (Braga, Leal, Carvalho, & Meireles, 2003). Many studies have provided evidence suggesting that curcuminoids possess a high spectrum of biological activities, such as anti-inflammatory, antioxidant and anticarcinogenic effects (Anto, George, Babu, Rajasekharan, & Kuttan, 1996).

The major constituent of turmeric oil, ar-turmerone (2-methyl-6-(4-methylphenyl)-2-hepten-4-one), is known to be a character impact compound, contributing to dry turmeric aroma (McGornin, 2002) and is used in pharmacy for its antibacterial, anti-fungal, antioxidant, antimutagenic and anticarcinogenic properties.

Turmeric extract exhibits an inherent pungent aroma which could mask the overall sensory desirability of the food products to which it is added. The application of technology capable of reducing the turmeric aroma at a competitive cost constitutes a fundamental factor for the wider use of turmeric extract in the food industry.

The utilisation of encapsulated extract, instead of free compounds, can effectively alleviate these deficiencies. Encapsulation is method employed to entrap active agents in a carrier to convert it to a useful form and to provide barrier between the sensitive bioactive substances and outer environment. Thus, this technology protects active compounds against evaporation, reaction or migration, masks odours, stabilises food ingredients and increases their bioavailability (Nedovic, Kalusevic, Manojlovic, Levic, & Bugarski, 2011).

Carrier materials used for protection of active ingredients must be food grade, biodegradable, able to form a barrier between internal phase and surroundings and provide required products without structural defects such as cracks, thin walls, or pores formed during or after processing (Zeller, Saleeb, & Ludescher, 1999). In this present work, brown rice flour was selected to encapsulate turmeric extract. Starch has been used as a wall material for encapsulation of flavour or extracts (Serfert, Drusch, & Schwarz, 2010). From the view of health, brown rice contains more dietary fibre than white rice. Some of the fibre, such as arabinoxylan and β-glucan, has a beneficial effect on the gut microbial composition in humans, suggesting that the anti-obesity and anti-diabetic effects of brown rice are related to the profile and activity of the intestinal microbiota (Kozuka et al., 2013).

The application of carbohydrate polymer to bind flavour using spray drying provides a physical entrapment of volatiles within a solid wall of hollow sphere to reduce their mobility (Zeller et al., 1999). However, pre-gelatinised rice flour for coating active substances has some disadvantages. Due to its stickiness, it does not afford easy work ability during encapsulation. In a preliminary study, we prepared brown rice flour solution for spray drying in the range of 1–10% (w/v) and found that 7% brown rice flour solution provided the optimal yield of product.

To suppress unpleasant odour, β-cyclodextrins (CDs) are beneficial to encapsulate volatile compounds prior to their use in foods. β-CD is a cyclic oligosaccharide consisting of seven glucose units linked by 1,4-glucosidic bonds (Paramera, Konteles, & Karathanos, 2011). The external part of the cyclodextrin molecule is hydrophilic whereas the internal part is hydrophobic. The guest molecules which are apolar can be entrapped into the hollow centre of the cyclodextrin molecule (Desai & Park, 2005). Encapsulation in CDs can mask the odour of fish oil (Serfert et al., 2010) and also stabilise fish oil (Del Valle, 2004). The encapsulation of turmeric extract using cyclodextrin as wall material has been reported to improve the sensory score in terms of colour and appearance (Haiyee et al., 2009).

In view of the above, this work aimed to investigate the flavour masking properties of blend wall material of BRF and β-CD for turmeric extract using spray drying. The effects of the wall material mass and β-CD concentration were studied using response surface methodology in order to optimise the process conditions. The microcapsules were characterised for their physical properties, curcuminoids encapsulation, and morphological characteristics. Volatile release in headspace was measured using gas chromatography coupled with a mass spectrometry (GC–MS). In addition, the odour intensity of microcapsules was evaluated by a trained sensory panel.