Encapsulation of strawberry flavour and physicochemical characterization of the encapsulated powders

Highlights

• Strawberry flavour was encapsulated by spray and freeze drying.

• Effects of spray drying parameters on aroma compounds were investigated.

• Increasing of MD ratio in wall material mixture increased aroma recovery.

• Microcapsules were generally spherical, smooth and homogeneous.

Abstract

This study was aimed to enhance the encapsulation stability of natural strawberry flavour using spray and freeze drying processes. Optimum spray drying conditions in terms of the wall materials (maltodextrin, soluble fibre, modified starch, β-cyclodextrin and arabic gum) and the inlet air temperature (130–190 °C) were determined using the response surface methodology where dependent parameters were minimum aroma release, maximum aroma recovery, drying yield and solubility. Particle morphology, particle size, bulk and tapped density analyses were also determined. The optimum conditions were found as; air inlet temperature: 190 °C, maltodextrin: 15.30%, modified starch: 1.83% and arabic gum: 12.87%. Optimum process yield and solubility of the microencapsulation were determined as 85.17 and 98.19%, respectively. Spray dried microcapsules were generally spherical, smooth and homogeneous while those obtained by freeze-drying were heterogeneous and spongy. Particle size of the spray dried samples (D₉₀ value: 22.91 μm) was much lower than the freeze dried samples (D₉₀ value: 326.83 μm).

Introduction

Natural or synthetic flavouring agents, which are used to improve the sensory quality of food by giving specific odour and aroma, have high economic values. Natural flavours are formed as a result of complex biological reactions dependent on various genetic factors [1]. A large number of volatile components in any fruit are responsible for the formation of fruit-specific flavours [2]. Orange, lemon and grapefruit aroma originates from terpenoids while esters and aldehydes are responsible to provide the aroma of apples, raspberries, cranberries and bananas. It is known that the aroma appears in bananas, peaches, pears and cherries during fruit ripening [2].

Flavour molecules having comparatively lower molecular weights are acids, alcohols, esters, ketones, aldehydes, etc. [1,3]. Esters, which are important functional groups responsible for flavour in fruits, generally defines the characteristic flavour of fruits. More than 300 compounds have been identified that contribute to the aroma profile of the strawberry. It has been reported that the variety, ripening, and environmental factors affect the aroma profile of strawberry fruit [2]. The main components of the strawberry flavours are esters, acids, aldehydes, alcohols and terpenes [4]. Sulfur compounds, acetals, furans, phenols, epoxides and hydrocarbons also contributes to the strawberry flavour. Among them, methyl/ethyl ester, furanones, C6-aldehydes and other C6-derived compounds are considered to be the main flavour responsible for strawberry flavour [[4], [5], [6], [7]]. The amount of these flavour compounds either decreases during the process and storage or lose their effectiveness by transforming into other substances [3]. Many researchers have tried to find different ways to keep the flavour constituents in the food samples. Different encapsulation methods have been developed to increase the storage stability of these sensitive flavour components.

Encapsulation is a process to produce capsules of different sizes [8] to protect the encapsulated material from undesirable reactions (oxygen, temperature and light) during processing or storage period [9,10]. There are different encapsulation methods such as spray drying, spray cooling/freezing, extrusion coating, fluid bed coating, liposome confinement, coacervation and centrifugal extrusion which are widely used in various industries [11]. Spray drying is one of the most used technique for flavour encapsulation. Continuous production capability, ease of use, low cost, wide selection of carrier materials, good retention of volatile components and final product stability are the most preferred reasons of spray drying method [[12], [13], [14], [15]]. This method has three main critical stages. First one is atomization that ensures the large surface area for maximum heat and mass transfer between air and atomized liquid particles. The second is the droplet formation where volatiles diffuse with water to the surface of the capsule. In the meanwhile, capsule surface is still underway as a selective membrane. So that the volatiles are released into the drying air. The last and the most losses occurs during the explosion of droplets when the water in the droplet reach the boiling point [16].

The choice of coating material to be used in the encapsulation is an important factor affecting the success of the process. The coating material is required to protect the core material by acting as a barrier against external influences and to prevent it from reacting with any other component. On the other hand, the carrier material must ensure higher emulsion stability, lower viscosity at high concentrations, allow film forming, release the flavour on time and at the desired location [11]. Some of the most used encapsulation materials in food industry are maltodextrins, arabic gum, modified starches, whey protein, cyclodextrin, cellulose [17] which are generally used in a combination to provide all the desired properties. Nevertheless, sensitive to the environmental conditions such as oxygen, temperature and light, flavour compounds lose their activity during processing or storage period. In order to minimize these restrictions during their usage, it is aimed to increase the stability of the flavours by encapsulation. There are several studies performed on encapsulation of flavours such as limonene [18] (Soottitantawat et al [19]; Sultana et al [20]), vanilla-raspberry [21], rosemary [22], and strawberry [23], and watermelon [24].

This study was aimed to optimize the wall material and the inlet temperature of strawberry flavour by spray drying. Maltodextrins, arabic gum, modified starches, β-cyclodextrin and soluble fibre were chosen as the wall materials with inlet temperature between 130 and 190 °C. The optimization conditions were determined by RSM with mixture design. In addition, strawberry flavour obtained at optimum wall materials conditions were also dried by using freeze drying method.