Effect of whey protein isolate and β-cyclodextrin wall systems on stability of microencapsulated vanillin by spray–freeze drying method

Highlights

• Spray–freeze-drying (SFD) technique used for microencapsulation of vanillin flavour.

• β-Cyclodextrin, whey protein isolate (WPI) and their combinations effects as wall materials was evaluated.

• Vanillin + WPI by SFD method exhibited better thermal stability than the spray drying and freeze-drying techniques.

Abstract

Vanillin flavour is highly volatile in nature and due to that application in food incorporation is limited; hence microencapsulation of vanillin is an ideal technique to increase its stability and functionality. In this study, vanillin was microencapsulated for the first time by non-thermal spray–freeze-drying (SFD) technique and its stability was compared with other conventional techniques such as spray drying (SD) and freeze-drying (FD). Different wall materials like β-cyclodextrin (β-cyd), whey protein isolate (WPI) and combinations of these wall materials (β-cyd + WPI) were used to encapsulate vanillin. SFD microencapsulated vanillin with WPI showed spherical shape with numerous fine pores on the surface, which in turn exhibited good rehydration ability. On the other hand, SD powder depicted spherical shape without pores and FD encapsulated powder yielded larger particle sizes with flaky structure. FTIR analysis confirmed that there was no interaction between vanillin and wall materials. Moreover, spray–freeze-dried vanillin + WPI sample exhibited better thermal stability than spray dried and freeze-dried microencapsulated samples.

Introduction

Vanilla is widely used as a flavouring compound in bakery, beverage, and ice-cream industries. Vanillin (3-methoxy-4-hydroxybenzaldehyde) is extracted from the pods of Vanilla planifolia through an expensive process. Approximately 50% of the world production of vanillin is used as an intermediate in the production of herbicides, antifoaming agents or drugs (Walton, Mayer, & Narbad, 2003). Sinha, Sharma, and Sharma (2008) reported the uses of vanillin as an antioxidant, anticarcinogenic, antimutagenic, and antisickling agent. Due to its phenolic character, it is also used as a chemical intermediate during the production of fine chemicals and pharmaceuticals (Claudio, Freire, Freire, Silvestre, & Coutinho, 2010).

Microencapsulation is a technique in which sensitive bioactive compounds (e.g., vanillin, probiotic bacteria, β-carotene and omega-3 fatty acids) are packed within a secondary material (e.g., protein, polysaccharide or lipids) to protect from oxygen, heat, light and to facilitate food fortification. The microencapsulated material is coined as core whereas the surrounding encapsulating agent is termed as wall material (Pillai, Prabhasankar, Jena, & Anandharamakrishnan, 2012). Whey Protein Isolate (WPI) is found to be a suitable wall material for microencapsulation of volatile compounds (Bae & Lee, 2008). WPI consists of three principal components such as β-lactoglobulin, α-lactalbumin and bovine serum albumin; moreover it exhibits excellent film forming abilities (Sliwinski, Roubos, Zoet, van Boekel, & Wouters, 2003). However, WPI has never been employed for the microencapsulation of vanillin. The other wall material like β-cyclodextrin, has been widely used for encapsulation in more than decade (Bhandari et al., 1998). Cyclodextrins are a series of cyclic oligosaccharides that are enzymatically derived from the starch employing CyD transglycosylase. β-Cyclodextrin comprises of 7-d-glucose units which are connected by α-1, 4 linkages. Further β-cyd structure resembles a thick walled bucket with a hydrophobic cavity and hydrophilic exterior. Weak forces such as van der Waals force, dipole–dipole interaction and hydrogen bonding help them to form an inclusion complex by entrapping guest molecule inside its cavity. Vanillin and β-cyclodextrin inclusion complex formation has been studied by Karathanos, Mourtzinos, Yannakopoulou, and Andrikopoulos (2007). Pena, Casals, Torras, Gumi, and Garcia-Valls (2008) have also investigated the vanillin release from polysulfone macrocapsules. Similarly, vanillin was encapsulated using carnauba wax to study the kinetics of vanillin release mechanism (Stojakovic, Bugarski, & Rajic, 2012). Tari, Annapure, Singhal, and Kulkarni (2003) have microencapsulated vanillin in starch based spherical aggregates of size 7.5–45 μm and it was prepared from amarnath, quinoa, rice and colocasia in presence of bonding agents such as gum Arabic, carboxy methyl cellulose, and carrageenan. However, retaining thermal stability of vanillin is a problem due to its very high volatility nature (Kayaci & Uyar, 2012). Thus, microencapsulation of vanillin can be solution for increasing the thermal stability of vanillin.

Spray drying and freeze drying are widely used for microencapsulation of various bioactive compounds and flavouring materials (Anandharamakrishnan, 2014). Microencapsulation of PUFA oils by spray drying leads to increased rancidity problems. On the other hand, freeze drying requires high residence time that leads to higher operating cost, which is the main hindrance for the utilisation of this technique. Hence, spray–freeze drying (SFD) is an effective alternative to spray drying and freeze drying techniques. SFD is a two-step process where the first step involves spray freezing, and the second one involves freeze drying (Anandharamakrishnan, Rielly, & Stapley, 2010). Currently, there are three types of techniques being used for spray freezing: (1) spray freezing into vapour, (2) spray freezing into vapour over liquid, and (3) spray freezing into liquid (Karthik & Anandharamakrishnan, 2013). Powders with large surface-to-mass ratio can be produced by SFD; furthermore wettability and dispersibility are the key factors and are important for the powder reconstitution (Rogers, Wu, Saunders, & Chen, 2008). Highly soluble due to large number of pores along with lower drying time makes SFD a highly appropriate technique for microencapsulation of sensitive compounds. Bioactive compounds which are thermally sensitive such as DHA algae oil (Karthik & Anandharamakrishnan, 2013), Tolbutamide (Kondo, Niwa, Okamoto, & Danjo, 2009) and probiotics cells (Dolly, Anishaparvin, Joseph, & Anandharamakrishnan, 2011) were efficiently microencapsulated by SFD technique.

The objective of this study is to apply spray–freeze drying technique to produce microencapsulated vanillin using WPI and β-cyclodextrin as wall systems. Further, the effectiveness of SFD technique was compared with SD and FD vanillin based on their morphology, particle size, moisture content, thermal stability, microencapsulation efficiency, and core to wall interaction.