Irène Allais

Fuzzy concepts applied to food product quality control: A review

Fuzzy logic is now a wide field of study and different tools have been developed over the last 10 years. Its implementation in food quality control for the food industry has been highlighted by several authors that have focused on different applications designed specifically for this task. This is especially true in the case of taking into account the reasoning process, expressed in linguistic terms, of operators and experts. Nevertheless, applications are still limited and few reviews on this topic are available. Consequently, the aim of this paper is to provide an overview of the application of fuzzy concepts to the control of the product quality in the food industry over the past 10 years. Future interesting developments and trends in this area are also emphasized.

Analysis of heat transfer during mist chilling of a packed bed of spheres simulating foodstuffs

Abstract Heterogeneity of heat transfer was studied in a packed bed of 8 mm spheres cooled by a two-phase flow composed of air and fine ( 8 μm diameter) water droplets. Local heat fluxes in the packed bed were measured in both single- and two-phase flow and analyzed as a function of water mass flow rate, the surface temperature of the spheres and air velocity. Heat transfer was enhanced in the two-phase flow: the maximum value rose to 2.8 under experimental conditions. The study shows that heat transfer depends on several factors: axial position, temperature difference, water mass flow rate and air velocity. A marked heterogeneity of heat transfer was demonstrated and was correlated with the local mass flow rate of the collected water.

Analyse du transfert thermique entre un cylindre et un écoulement d'air faiblement chargé en gouttelettes d'eau

Abstract Chilling of fruit and vegetables by forced air convection is slow and causes a weight loss of several percent. ‘Mist-chilling’, which uses a two-phase flow composed of air and suspended water droplets as a cooling medium, can reduce these drawbacks. In this process, the water supply must be controlled to avoid water excess at the surface of the product. It is known that the water supply must be high at the beginning of the treatment, when the products are still warm, and must be reduced during treatment to avoid water accumulation, which can cause spoilage of vegetable products. We measured heat-transfer between heated cylinders and two-phase flow. We studied the influence of several factors: diameter of the cylinders, temperature of surface and captured water mass flow rate. When the captured water mass flow rate is low, all the captured water evaporates and the analytical prediction given by the thermal balance agrees well with experimental data. As the captured water mass flow rate increases, the wet area on the cylinder surface increases. Water excess appears when the area of evaporation reaches almost 50% of the total surface of the cylinder.

Formalization of at-line Human Evaluations to Monitor Product Changes during Processing: The Concept of Sensory Indicator

Sensory characteristics of food products are essential for consumers. It is a challenge for firms to maintain these characteristics constant, with as few variations in quality as possible. The control of quality properties and in particular sensory ones can be carried out using reliable process control strategies. Nevertheless, classical control approaches can rarely be used in food processes due in particular to the lack of real-time, reliable instrumental sensors, which limits available information on the product, and to poor understanding of the interactions between food and process. The scarcity of suitable on-line sensors is closely related to the variability of the raw material, the complexity of the biological phenomena during processing and the severe constraints that sensors must satisfy, such as hygiene, high humidity, and so on. As a consequence, some food product properties are very difficult to be quantified during food manufacture [11]. However, various solutions have been explored to overcome this problem: sensor design and adaptation, off-line measurements, software sensors [21]. Moreover, human evaluation is widely accepted as a tool for the evaluation of the quality of food products: operators play a major role in process control, since they take into account not only the information from sensors but also that from their own senses [20]. They can detect small changes in product characteristics such as cookie color after baking [12] thanks to their process knowledge and experience.

The Fuzzy Symbolic Approach for the Control of Sensory Properties in Food Processes

End products must conform to the characteristics defined in their specifications. These characteristics include sensory properties, which are essential because they influence the choice and the preference of consumers. It is important to take them into account for their control when manufacturing products. Therefore, in food industry, these properties must be controlled close to the manufacturing line by implementing adapted measurement and process control.

Use of Response Surface Methodology to Study the Influence of Water Content and Air Pressure on Cake Batter Quality

The first aim of the study was to model the influence of water amount and air pressure on various batter properties using Response Surface Methodology. Batter quality was assessed through density, water content, colour, spreadability and fluorescence spectra. Quadratic models using two variables well represented spreading time, water content and final temperature, but they failed to fairly represent initial density, overrun and L*a*b* values. In addition, simplified models using a single variable also well represented the data: final density was modelled by a linear equation involving pressure, whereas initial density, water content and final temperature were modelled by a linear equation involving water amount. Spreading time was modelled using a quadratic equation using water amount. Experimental results were compared with expertise rules used by operators to control the industrial process. Indeed, operators often used water amount and air pressure as controlling variables. It was found that experimental results were in agreement with expertise rules. The second aim was to investigate the link between smart lab-measurement methods such as fluorescence spectroscopy and simple macroscopical properties used by operators such as water content, density, spreading time and colour. By applying hierarchical clustering analysis to NADH and tryptophan merged spectra, batter samples manufactured at various water amounts and pressure levels were clearly separated at a high level of discrimination. Neither water content nor spreading time were satisfactorily predicted from NADH or tryptophan spectra using PLS.