Design+of+experiments

The experimental design in a screening experiment involves all the factors at two levels: upper and lower. In the case of the ‘Soya yogurt drink with kiwi flavour’, the four **factors** are the following: **i)** //water//    **ii)** //kiwi juice percentage// **iii)** //sugar percentage//    **iv)** //cow’s yogurt percentage//
 * Experimental design**
 * **Screening experiment**

The 2 levels for each factor are presented on the Table below:
 * < **Factor** ||= **Lower Limit** ||= **Upper Limit** ||
 * < % cow's yogurt ||= 20 ||= 50 ||
 * < % water ||= 13 ||= 34 ||
 * < % kiwi juice ||= 8 ||= 15 ||
 * < % sugar ||= 6 ||= 15 ||

Two limits were set for all the four factors (Table 1) and all possible combinations were examined ( 24 =16 in total). These ranges were selected according to technical specifications and after a preliminary research on similar products in the market. The 16 samples were evaluated for four selected sensory attributes defined by the user needs-and-wants study on Unit 2. These **attributes** were the following: **i)** //thickness//    **ii)** //milk flavour// **iii)** //kiwi flavour//    **iv)** //sweetness// In addition, the samples were evaluated for overall acceptability.

Thickness is correlated with the percentage of water, milk flavour with the percentage of cow’s yogurt and kiwi flavour with the percentage of kiwi juice.

The sensory panel was consisted of 32 untrained assessors. A balanced complete block was used and the test was divided into two sessions, 8 samples per session. The 9-point hedonic scale was used for the evaluation where 1 corresponds to "Dislike extremely' and 9 to "Like extremely".

The questionnaire was designed using the software Compusense® five and the responses were collected on the computer.

An optimisation experiment was conducted in order to determine the optimum region and also the most important factors to be identified in order to achieve the best possible response. Two **factors** were examined (based on screening experiment results) in three levels and they were the following:
 * **Optimisation experiment**

**i)** percentage of cow’s yogurt

**ii)** percentage of kiwi juice

The percentage of both sugar and water was kept constant at 10% and 20% respectively.

The 3 levels for each factor are presented on the Table below:
 * **Factor** || **Lower Level** || **Medium Level** || **Upper Level** ||
 * = % cow's yogurt ||= 7.2 ||= 14.7 ||= 22.2 ||
 * = % kiwi juice ||= 8 ||= 10 ||= 15 ||

The sensory attributes were the same as in the screening experiment.

The two factors were examined in the three levels in all possible combinations - LL, LM, LH, ML, MM, MH, HL, HM, HH - (Low-L,Medium-M, High-H).

The sensory panel was consisted of 54 untrained assessors. A balanced complete block was used.The 9-point hedonic scale was used for the evaluation where 1 corresponds to "Dislike extremely' and 9 to "Like extremely".

The questionnaire was designed using the software Compusense® five and the responses were collected on the computer.

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