# Characterization of Quality Properties in Spoiled Mianning Ham
## 1 Introduction  
Dry-cured ham is a traditional fermented meat product that has a long history of development. Dry-cured ham is a raw meat product made from whole pork legs with bones, skin, and claw tips that have been cured, washed, air-dried, fermented for a long time, and shaped [1]. The production of dry-cured ham is more common in Mediterranean countries such as Italy, Spain, or Portugal [2]. In addition, some European countries also have a tradition of dry-cured meats, such as Croatian Prsut and Polish Kindziuk or Kumpiak podlaski [3; 4]. Several studies have reported sensory attributes and volatile compounds in qualifying dry-cured hams, especially in Spanish, Italian, and French dry-cured hams, and also Slovenian dry-cured ham [5]. Additionally, dry-cured ham has been largely studied for its physicochemical and sensory characteristics depending on different processing technologies [4]. Mianning ham is a famous fermented meat product in Sichuan, China, protected by the National Geographical Indication, made from plump pig hind legs that are repaired, cured, washed and dried, and fermented. The common types of spoilage in dry-cured ham are deep spoilage and vein defects (surface rot). Deep spoilage, which is typical of the winter months, is caused by _Enterobacter agglomerans_,_Proteus vulgaris, Serratia liquefaciens,_ and _Clostridium_ spp. and characterized by the smell of sulfur compounds [6]. Some odors, such as potato, benzoic acid, and walnuts, can be found near the femoral head. Deep spoilage is the most important type of deterioration, where the growth of microorganisms causes the breakdown of proteins, resulting in a paste-like texture of the ham and the production of peptides, amino acids, amines, ammonia, sulfides, alcohols, aldehydes, ketones, and organic acids. It gives the ham an unpleasant and unacceptable taste [7,8]. Surface spoilage which represents 40% of the total dry-cured ham defects, is caused by a microorganism that was recently identified as _Marinilactobacillus psychrotolerans_[9].  
Mianning ham is produced using natural fermentation and without the use of any preservatives. The quality of the ham relies entirely on the penetration of salt and dehydration. Therefore, during the production and maturation of ham, it is susceptible to microbial contamination, leading to spoilage and deterioration. It has been suggested that this type of spoilage is caused by microflora, especially bacterial contamination, and the corresponding strains have been isolated based on culture methods [10]. It was also found that fungal toxins and metabolites can cause off-flavors at various stages of ham production and processing, with _Penicillium, Aspergillus_, and _Ulva_ being the most common, negatively affecting the quality of ham and causing it to spoil [11]. Most researchers attribute the cause of spoilage to bacteria [12], while others point to the influence of meat's own enzymes on spoilage [13].  
The microbial community structure and volatile flavor substances associated with spoilage of Mianning ham have not been reported. Therefore, the present work is on the differences in physicochemical indicators, microbial communities, and volatile compounds between different spoilage types of Mianning ham and normal Mianning ham. It uses physicochemical properties and volatile flavor substances to distinguish normal Mianning ham from rotten Mianning ham and to identify the main microorganisms that cause the rottenness of Mianning ham. This is of great importance to the development of the Mianning ham industry.