Opportunities for the development of clean label probiotic ice cream : a thesis presented in partial fulfilment of the requirements for the degree of Master of Food Technology, Massey University, Albany, New Zealand

Abstract

In ice cream manufacture, stabilisers and emulsifiers are used as additives to produce products with desirable properties. Typically, mono-/diglycerides, polysorbate, and several gums such as guar gum, locust bean gum and carboxymethyl cellulose are used to emulsify and stabilise ice creams, respectively. Consumers have long been skeptical about the presence of additives with unfamiliar and complex chemical compounds with E-numbers on the label of food products and consider products with simple and natural ingredients as healthier. Therefore, there is need to identify potential ingredients to replace the commonly used additives in ice cream and produce products which may be more appealing to consumers. In this study chia seed gum (mucilage) (CSG) and sweet cream buttermilk (SCB) were the two ingredients identified to replace the commonly used stabilisers and emulsifiers in ice cream, respectively. The addition of a probiotic culture was also considered to produce functional ice cream with clean label as well as probiotic properties. The study commenced with the extraction of CSG, followed by four integrated phases which involved the production of prototype ice creams. The extraction of chia seed mucilage from chia seed using a seed:water ratio of 1:20 at 50°C/40 min, yielded 3.40±0.16% (w/w) of the dried CSG (9.9% moisture (w/w)). The pH of the extracted mucilage before drying was 6.14±0.07. In Phase I, the extracted CSG was added to ice cream at three concentrations (0.1%, 0.2% and 0.3% (w/w)) to replace the commercial stabilisers. Physico-chemical properties (pH, viscosity of the ice cream mix, overrun, fat globule size distribution, destabilised fat index, meltdown rate and hardness of ice cream) were determined in the prototype ice creams. The frozen desserts were also evaluated by a focus group of six sensory panelists. The most acceptable ice cream contained 0.2% CSG (w/w) which was characterised by an overrun of 103.10±0.47%, 41.00±5.35% destabilised fat index, 40.66±8.87% fat globule size distribution (d4,3) and low meltdown rate (0.96±0.14 g/min) compared to the ice cream which contained guar gum (commercial stabiliser). The hardness of the ice cream was 40.06±7.23 N. The ice cream had desirable hardness, smooth texture and creamy mouthfeel without sensation of ice crystals and off-flavour.

In Phase II, the emulsifying ability of CSG was investigated in the ice cream formulation selected from Phase I (F2) in the absence of mono-/diglycerides (MDG) (commercial emulsifier used in Phase I). The absence of MDG from F2 did not change the viscosity of the ice cream mix (F7) whereas the overrun, destabilised fat index and fat globule size (d4,3) of the ice cream decreased to 77.86±5.83%, 8.43±1.55% and 28.15±36.10%, respectively. The meltdown rate and hardness increased to 1.61±0.10 (g/min) and 93.88±15.5 (N), respectively. The sensory properties of F2 were more desirable to the focus group than F7. Sweet cream buttermilk was used in Phase III to improve the emulsification attributes of the ice cream (F7) due to the absence of MDG. Therefore, in this Phase the emulsifying properties of SCB was investigated when it partially substituted the skim milk powder and comprised 25% and 50% (w/w) of the nonfat milk solids (NMS) in ice cream. The addition of SCB did not affect the viscosity of the ice cream mix but it enhanced the overrun to 82.71±1.61% and 88.90±0.10% when constituted 25% (w/w) (F8) and 50% (w/w) of the NMS (F9), respectively. The increase in the concentration of SCB decreased the rate of meltdown to 1.57±0.05 (g/min) in F9 and 1.60±0.08 (g/min) in F8. The destabilised fat index and fat globule size distribution (d4,3) of the ice cream decreased to 8.03±1.31% and 6.74±0.30% in F8 and 4.43±3.84% and 22.53±2.12% in F9, respectively. The hardness of F8 and F9 increased to 102.17±41.00 and 101.85±33.00 N, respectively. The focus group selected F9 due to its smooth texture, desirable hardness, mouthfeel and melting attributes. F9 was selected as the best formulation based on physico-chemical and sensory results. In Phase IV, the effect of the addition of 10% milk fermented with probiotic culture (Lactobacillus acidophilus La-5) (w/w), to the ice cream mix (F10) after aging was investigated. The addition of the probiotic culture slightly enhanced the viscosity of the ice cream mix whereas the overrun and meltdown rate of the ice cream decreased to 88.49±0.54% and 1.24±0.04 (g/min), respectively. Compared to the rest of the formulations, the ice cream mix of F10 showed a high fat globule size distribution (d4,3) (12.90±0.90%). Relative to F9, formulation F10 had a higher destabilised fat index (11.96±1.44%) but this ice cream had a lower fat globule size (d4,3) (13.83±2.02%) and hardness (84.20±18.70 N). In this Phase, the pH, viable cell counts and the consumer acceptance (using a 9-point hedonic scale) of the ice cream (F10) were evaluated after hardening (48 h) and prolonged storage (30 days) at -20 °C. The pH, viable cell counts and overall mean sensory acceptability scores for the ice cream after hardening (48 h) were 6.27±0.01, 1.15×107 CFU/mL and 7.10±0.97 (n=24) whereas the respective values were 6.27±0.06, 1.07×107 CFU/mL and 7.27±1.14 (n=28) respectively, after 30 days of frozen storage. The sensory characteristics of the ice cream were stable during storage and the survival cell counts were above the recommended minimum limit (106 CFU/mL) required to confer probiotic health benefits. The overall results indicated that CSG can be used as stabiliser and emulsifier in ice cream but the overrun would be low. For producing ice cream with higher overrun, it would be desirable to add SCB. Also, results showed that a probiotic culture can be added to ice cream which improves the health attributes of the frozen dessert as well as decreases the meltdown rate of the ice cream. Further study is required to determine the contribution of CSG, SCB and the probiotic culture to the microstructure of ice cream using cryo-scanning electron microscopy.