Proximate, Physicochemical and Sensory Attributes of Stirred Yoghurt Flavoured with African Star Apple Pulp (Chrysophyllum albidum)
Authors: Eze C. M. , Aremu K. O. , Asogwa I. S. , Obeta N. A. , Joseph C. D. , Ibrahim A. N. 
Published: July 2020

Aims: To Investigate the Proximate, Physicochemical and Sensory attributes of Stirred Yoghurt Flavoured with African Star Apple Pulp (Chrysophyllum albidum).

Study Design: Randomized Completely Block Design (RCBD).

Place and Duration of Study: Department of Food Science and Technology, Faculty of Agriculture, University of Nigeria, Nsukka, Enugu State Nigeria between December 2018 and October 2019.

Methodology: The materials, as well as the other ingredients for the preparation of the flavoured stirred yoghurt (African star apple, skimmed milk, sugar, and Starter culture (YoghurmetTM) were sourced from Ogige main market in Nsukka Local Government Area of Enugu State, Nigeria. The African star apples were sorted to separate the fresh and good fruits from insect-infected and mechanically damaged ones. The fruits were thoroughly washed with water to further eliminate adherent dirt so as to obtain sand-free fruits. Peeling of the fruits was done to remove the back. Each of the peeled fruits was cut into two in order to remove the seeds thereof. The pulps were carefully removed manually with knife and the pulps were blended using a blender after which pasteurization at 83°C for 3 minutes was carried out before being added to the processed yoghurt. Yoghurt flavoured with pasteurized African Star Apple pulp was produced by homogenizing, pasteurizing the milk product followed by cooling to inoculation temperature which is optimum for the starter culture (Yoghurmet). The inoculated milk was made to undergo fermentation after which the pasteurized African star apple pulp at different proportions was added to formulate five samples of stirred yoghurt.  The formulation ratios of yoghurt to African star apple pulp were as follows: 100:0, 90:10, 80:20, 70:30, 60:40, 50:50. The flavoured yoghurt samples were mixed, smoothened and packaged for cold storage.

Results: The result of physicochemical analysis revealed that viscosity (2.65 ± 0.06 cP – 3.25 ± 0.06 cP), total solids (22.35 ± 0.06% - 30.20 ± 0.06%), total titratable acidity (0.36 ± 0.00% -   0.39 ± 0.01%) and pH (5.20 ± 0.00 - 5.40 ± 0.00) differed significantly (P < 0.05) as the control sample YC (100:0) was compared with the yoghurt samples flavoured with African star apple pulp. The proximate parameters -  Carbohydrate (11.20 ± 0.64% - 21.41 ± 0.10%), moisture content (71.53 ± 0.05% - 80.36 ± 1.17%) and ash content (1.30 ± 0.00% - 1.98 ± 0.03%) of the formulated yoghurt samples showed significant (P < 0.05) decrease as concentration of ASA pulp increased while crude protein (3.67 ± 0.01% -  4.92 ± 0.02%), fat (1.21 ± 0.02% - 2.72 ± 0.03%) and crude fibre (0.20 ± 0.00% - 1.40 ± 0.00%) showed significant (P < 0.05) increase with increasing concentration of ASA pulp. Among the formulated yoghurt samples, sample YP1 was the most preferred with respect to color (7.25 ± 0.91), taste (7.25 ± 1.07), aftertaste (7.00 ± 1.17), mouthfeel (6.95 ± 1.40), flavour (7.25 ± 0.64) and overall acceptability (7.30 ± 0.73).

Conclusion: Although the control sample YC (100:0) had most preferred sensorial qualities, yoghurt samples flavoured with African Star Apple pulp would rival the “used-to plain yoghurt” with improved awareness, and usage lower than 20% of the ASA pulp in yoghurt samples would maintain the product’s acceptability among the variety-loving dairy consumers.