Article pp.138-141 du Vol.23 n°1 (2003)

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138-141 Sci. Aliments 23(1), 2003 C. Curt et al.

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Determination of functioning conditions for the meat emulsification process using at-line

human evaluations and the Simplex method

C. Curt¹ V. Leblanc¹, I. Allais¹, N. Perrot¹, V. Chevallereau¹, G. Trystram²

1 – INTRODUCTION

Sensory characteristics of food products are essential for consumers: it is a challenge for firms to provide them products with expected sensory properties.

Various optimisation strategies exist: indirect approaches that rely on a model and sequential approaches that are judicious since the intermediary stages are themselves solutions, the stopping of the method being performed on the basis of criteria such as the maximum number of trials or closeness of the sample in comparison with the reference. Among these sequential approaches, the Sim- plex method (1) have been used to optimise processes (2-3) and the formulation of food products (4-6). The first point of an optimisation problem processing consists in the determination of a performance function that represents the characteristic that must be targeted, maximised or minimised for instance. This point raises problems: some food product properties are very difficult to quan- tify during food manufacture by sensors. Human knowledge is widely accepted as a tool for the evaluation of the quality of food products. We have described a method that fits with the formalization of human measurements made at line (7).

The aim of the present study is to determine functioning points for chopping operation that lead to a product with expected characteristics using the Sim- plex method and human measurements. The action variables used are chopping duration and speed.

1. Cemagref - Équipe Automatique et Qualité Alimentaire, BP 50085, 63172 Aubière Cedex.

Tél : 33+(0)4.73.44.06.64 - Fax : 33+(0)4.73.44.06.97 - corinne.curt@cemagref.fr 2. ENSIA – 1, avenue des Olympiades, 91744 Massy Cedex.

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Determination of functioning conditions for the meat emulsification process… 139

2 – MATERIALS AND METHODS

2.1 Materials and process

Pork lean meat and backfat were frozen separately at -20˚C during 3 days prior to use. They were thawed at 4˚C during 24 hours. The emulsification equi- pment consisted in a 30 L cutter (CDH, France) equipped with a temperature control system composed of a double jacket vat and a water-bath at a fixed temperature (18˚C). At the beginning of the trial, all the raw materials (lean meat:

1000 g, backfat: 1000 g, ice: 600 g, polyphosphate: 60 g, salt: 50 g, seasoning:

40 g, colouring: 3 g) are premixed in the bowl (1 min-500 rpm; 1 min-1000 rpm).

Emulsification duration and speed are then determined by the Simplex algorithm.

2.2 Calculation of the chopping degree

The calculation of the chopping degree (CD) has been developed using logical equations that rely the inputs and the outputs of a system in a symbolic way (8). Inputs are sensory indicators and an instrumental measurement, the temperature at the end of the chopping operation and the output is the chopping degree. Thirty-four logical equations allow the calculation of CD expressed between 1 (poor degree of chopping) to 5 (excellent degree of chopping). Four sensory indicators have been collected and formalized: fat particles size, size homogeneity, firmness and sticky property. These sensory indicators are assessed at the end of the chopping phase on a category scale. Logical equa- tion is expressed as for instance: “a product that presents a firmness assessed as “medium” and a fat particles size assessed as “medium” has a chopping degree of 4”.

2.3 Yield

The yield was determined at the end of the chopping: three samples of emulsion (W₁ = 40 g) were stuffed in centrifugation tubes and then placed during 30 min in a water-bath at 70˚C. After cooking, liquids which exude were eliminated and « solid emulsion » was weighted (W₂). Yield (%) was expressed as Y = (W₁ / W₂) _✕ 100.

2.4 Simplex algorithm

Let us consider a process depending on n continuous parameters. The res- ponse of a trial is represented in a n-dimensional factorial space as a point which coordinates are the values of the n parameters for the corresponding trial. A simplex is a group of points that frames a regular geometric figure. It represents the responses of (n+1) different trials (9). The evolution is performed by the elimination of the worst point that is replacing by its symmetrical point with respect to the hyperface containing the other points. Several criteria must be defined:

• the constraints: the duration is set between 1 min and 10 min, the mixing speed is bounded between 500 rpm and 3500 rpm;

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140 Sci. Aliments 23(1), 2003 C. Curt et al.

• the initial simplex that establishes the initial position in the experimental space [T1(1000 rpm, 3 min), T2 (1500 rpm, 3 min), T3 (1500 rpm, 2 min)]

and the evolution step between two trials. The duration step has been set at 1 min and the speed step at 500 rpm.

• the stopping criterion. Two criteria have been determined: the number of trials is limited to 20 and we are looking for the closest value of 5.

3 – RESULTS

The progression of the optimisation of the CD value is shown on Figure 1. It has been carried out by height trials. The stopping of the algorithm has allowed obtaining a local maximum point (T6): the batter obtained at T6 presents a CD value of 4.8 out of 5. The optimal conditions established at the stopping of the Simplex algorithm are the following: the mixing duration is 3 min and the speed is 2000 rpm. All the directions from T6 gave worse values of CD. Moreover, several additional trials have been performed all around the optimum point and within unexplored areas of the experimental space. The results confirm that among all the points, there is no better result than T6. Moreover, the area of maximum yield corresponds to the area determined as optimum by the Simplex method: it is maximum at T6 and is equal to 98.5 %.

Figure 1

Progression of the Simplex

CD values for the worst point (T1) and the best point (T6) are indicated in brackets

0 500 1000 1500 2000 2500 3000

0 1 2 3 4 5

Duration (min) (a)

0 1 2 3 4 5

Duration (min) (b)

Duration (min) (c) 0

500 1000 1500 2000 2500 3000

Speed (rpm)

0 500 1000 1500 2000 2500 3000

Speed (rpm)

0 1 2 3 4 5

Duration (min) (d) 0

500 1000 1500 2000 2500 3000

Speed (rpm)

T1 (3,2)

T2 T7

(4,1)

T6 (4,8)

T8 (4,1) Wrong direction Wrong direction

Wrong direction

T5 T4

T3 T2

T4 T2

T1 T3

T3 T2

T6 T4 T5

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Determination of functioning conditions for the meat emulsification process… 141

4 – CONCLUSION

The application of the Simplex method to the chopping operation has allowed the determination of the processing conditions assessed as two process parameters, mixing duration and speed, that lead to a targeted product.

The introduction of sensory indicators allows an optimisation of sensory quality during manufacture what is usually difficult considering the lack of sensors assessing this type of characteristics.

5 – AKNOWLEDGEMENTS

The authors would like to thank SARL Géret & Fils for its greatly appreciated co- operation and Région Auvergne for its financial support.

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