Zein nanoparticle stabilized Pickering emulsion enriched with cinnamon oil and its effects on pound cakes

Highlights

• Zein stabilized Pickering emulsion could replace 20% butter in pound cakes.

• Cinnamaldehyde may interact with amino group of zein at oil-water interface.

• The storage modulus of Pickering emulsions increased as the EO addition increased.

• Addition of 5 and 10 g EO extended the shelf-life for 4 and 12 days, respectively.

• Emulsion of 20 g ZNS+15 g oil+5 g EO didn't alter the texture and colour of cakes.

Abstract

Pickering emulsion enriched with cinnamon essential oil (EO) was applied to partially replace butter in pound cakes and to inhibit mold growth. Pickering emulsions stabilized by zein nanoparticles were dominated by elasticity (G' > Gʺ), indicating the formation of gel-like network microstructure. The aldehyde groups of cinnamaldehyde may interact with amino groups on zein nanoparticles at oil-water interface to enhance the viscoelastic properties of Pickering emulsions, which explained the increased storage modulus as the amount of EO increased. Pickering emulsion of 20 g zein nanoparticle solution (ZNS) +20 g sunflower oil significantly increased the hardness of pound cakes, while Pickering emulsion with 5 g EO addition maintained the texture and colour compared with control group. EO also exerted antimicrobial effect to pound cakes, as the yeasts and molds of 5 g and 10 g EO emulsion added cakes were 1.55 and 1.42 log CFU/g after 12-day room-temperature storage compared with 2.96 log CFU/g of control group. To conclude, Pickering emulsion of 20 g ZNS+15 g oil+5 g EO showed the best effect to replace 20% butter in pound cakes to lower the calorie intake and extend the shelf-life without altering the texture and colour.

Introduction

Pickering emulsion is an emulsion stabilized by amphiphilic macromolecules, such as proteins and polysaccharides, which will form steric elastic film to reduce the interfacial tension, making the emulsion elastic and solid-like (Xiao, Wang, Gonzalez, & Huang, 2016). It has been reported that Pickering emulsions can be stabilized by prolamin colloidal particles, such as gliadin, zein, kafirin, etc (Xiao, Li, & Huang, 2016). Zein, a low cost prolamin, is comprised of hydrophobic and hydrophilic amino acids, which can be used to stabilize Pickering emulsions.

Pound cake is a very popular dessert and snack food due to its flavour and mouthfeel. However, butter cake is also known as high caloric products because of the excessive fat content, which is around 15.8%–16.7% (w/w) (Rios, Garzón, Lannes, & Rosell, 2018; Samapundo, Devlieghere, Vroman, & Eeckhout, 2016). There are studies to replace butter with palm oil, a saturated fatty acid which is rich in carotenes and tocopherols, but high intake of palm oil may cause obesity and cardiovascular diseases (Mba, Dumont, & Ngadi, 2015). Rapeseed oil, rich in mono and unsaturated fatty acids, was applied as butter replacer, which leads to compromise of texture and flavour (Jahreis & Schäfer, 2011, chap. 114, pp. 967–974). The semisolid texture of Pickering emulsion may enable it to be a promising fat replacer while maintain the texture and other organoleptic properties of pound cakes due to its network nanostructure, moisture content, and elastic properties (Berton-Carabin & Schroen, 2015; Yano et al., 2017).

Pound cake is also prone to deteriorate due to microbial growth, especially mold contamination (Ju et al., 2018). Natural preservatives have drawn great attention to replace chemical preservatives to improve the quality of butter cake and extend shelf-life. For example, olive leaf extract rich in phenolic compounds were applied to prevent lipid oxidation of baked snacks (Difonzo et al., 2018). However, phenols may cause bitterness of the baked foods. It was also reported that adding flaxseed oil or milled flaxseed may improve oxidative stability of baked goods (Edel, Aliani, & Pierce, 2015). Essential oils extracted from spices, such as cinnamon and clove, have demonstrated wide spectrum of antimicrobial activity against spoilage bacteria and food-borne pathogens (Goñi et al., 2009). Cinnamon and clove essential oils have been used to inhibit mold growth on baked foods, and it has been found that cinnamon oil showed better inhibitory effects on mold growth compared with clove oil (Ju et al., 2018). Cinnamon essential oil has been reported to prolong the shelf-life of green bean cake in normal package by 9–10 days (Echegoyen & Nerín, 2015; Ju et al., 2018).

In this research, cinnamon essential oil (EO) was enriched in the oil phase of a Pickering emulsion to inhibit the mold growth on pound cakes to extend its shelf-life. The effects of EO addition on the rheological properties, particle size distribution and nanostructure of Pickering emulsions were evaluated. Furthermore, the impacts of Pickering emulsion addition on the texture, odour and microbial growth of pound cakes were studied.