## 2 Materials and Methods
### Experiment on the Separation of Raisins from Adhered Foreign Object
#### 2.1.2 Experimental Design  
Raisins are sugar-rich agricultural products, with Thompson seedless raisins typically exhibiting a moisture content of 10-20%. The predominant sugar components in raisins are glucose and fructose [13]. Due to the relatively low solubility of glucose, prolonged storage or improper preservation conditions lead to gradual sugar precipitation on the raisin surface, forming visible sugar crystals. This not only deteriorates the visual texture but also causes the surface sugars to dissolve under temperature fluctuations, creating a highly viscous syrup-like layer. This layer facilitates adhesion between raisins or between raisins and foreign objects, making separation difficult. Elevated temperature and humidity exacerbate this adhesion phenomenon.  
Previous studies have demonstrated that polymers generally undergo a glass transition from rubbery to glassy states as temperature decreases. In the glassy state, polymer chain segment motion is frozen, allowing only small-scale molecular movements and minimal  
Figure 3: Experimental samples.  
Figure 2: Proportion of different types of foreign objects.  
deformation under external forces [14]. Although raisins themselves are not polymers, their sugar components exhibit glass transition behavior under specific conditions. Water acts as a plasticizer that reduces the glass transition temperature (Tg) of raisins [15]. Foods with moisture content below 20% typically achieve complete glass transition, while those above 20% or low-concentration solutions form partially crystalline glassy states [16]. Glassy sugars exhibit relatively ordered molecular arrangements, forming quasi-solid structures. When subjected to external forces like impact or stretching, these structures lack plastic deformation capacity, leading to stress concentration-induced cracks that propagate rapidly, resulting in brittle fracture. For sugar solutions, slow cooling allows sufficient molecular diffusion for ordered crystallization, whereas rapid cooling increases system viscosity sharply, hindering molecular motion and lattice arrangement, thereby achieving glassy states.  
Based on these findings, the experiment first employed rapid freezing to bring prepared samples to target temperatures of 0 \({}^{\circ}\)C, \(-\)10 \({}^{\circ}\)C, \(-\)20 \({}^{\circ}\)C, \(-\)30 \({}^{\circ}\)C, \(-\)40 \({}^{\circ}\)C, and \(-\)50 \({}^{\circ}\)C. Textural properties were then analyzed using a TA-XT Plus Texture Analyzer (Stable Micro Systems, UK, shown in Figure 4). Raisin samples were placed on the analyzer platform and subjected to compression tests under different freezing conditions using a cylindrical probe (TA/36R) at a test speed of 1.0 mm/s with auto-trigger mode. Average hardness values were recorded for each temperature condition. Tensile tests were conducted to measure the average pulling force required to separate raisins from foreign objects, serving as an adhesion indicator. Finally, combining textural data and adhesion results, separation experiments were performed using two common manual methods--percussive tapping and rolling compression (rubbing)--to determine the optimal freezing temperature and separation technique.