Kinetic functions, optimizing model and definition of "Huohou" for Chinese cooking

As the most important technical term of traditional Chinese cuisine, "Huohou" originally means the degree of heating, and also implies the appropriate termination of cooking. There is not unanimous understanding of "Huohou" in the published literature; some of the existing concepts were mostly descriptive without theory support, and several of them contain conspicuous mistakes. In this thesis, as the third of a series of six theses, the author tried to define "Huohou" with quantitative equations on the bases of kinetics and heat transfer, and reveal the key principle of Chinese cooking technology. The quality factors of maturity for finished products in cuisine can be characterized by one or more indicators about flavor chemistry, pigment chemistry, texture, microbiology, toxicology, etc. Usually, the quality factors are merely for solid particles. Transient heat transfer is the basic characteristic of solid particles in cuisine, hence there are different temperature histories in different heat transfer characteristic dimensions of a particle; thus, the intraparticle quality distribution is brought about. Ordinarily, the last mature point is the coldest spot in the food system, which should be the center of particles in general. Along with the food center reaching maturity, the excentral part has already been overheated, particularly the surface, where quality deterioration is produced. Therefore, it was suggested that the goal of "Huohou" is to minimize quality degradation via overheating while food materials are heated to maturity. In order to express the degree of maturing quantitatively under variations of temperature, several novel kinetics functions are put forward for the cooking process, including maturity value (M value), maturity time tM and overheated value (O value). The maturity value was physically defined as the equivalent heating time to a reference temperature when cooking quality reaches maturity, and maturity value is the C value at maturity time. The overheated value was physically defined as the equivalent heating time that forms quality deterioration for relative reference temperature when cooking quality reaches the overall maturity. Maturity values and overheated values may appear in different spatial positions in the food system in cuisine, such as surface maturity value, volume average maturity value, surface overheated value and volume average overheated value. According to the experience of other thermal processes, like thermal sterilization, we extrapolated that there are the optimal conditions of heat transfer operating for cooking quality in thermal process of liquid-particles in traditional Chinese cuisine only if Z value of maturation quality factor and Z value of overheated quality factor are not the same. Based on the governing equations for heat and mass transport processes, an optimal model was constructed for mixture of liquid and particles in typical Chinese cuisine, which has a constraint condition as the C value equals maturity value; an objective condition to minimize the overheated value; and design variables including the parameters of heat transfer controlling, such as liquid temperature and the heating power. Thus, "Huohou" was synoptically defined as the cooking-temperature regimes that can enable cooking quality to achieve optimal, and it was dynamically defined as the cooking operation minimizing the overheated value while ensuring that the cooking value reaches maturity.