| Shanxi aged vinegar (SAV) is one of the most four famous cereal vinegars in China,which Lusing a spontaneous solid-state fermentation technique. While one of the most universal phenomenon in cereal vinegars using solid-state fermentation in our country is that vinegars always forming sediments in shelf life, which as a result, impacts the sensory quality of vinegars badly. Ingredients of the traditional cereal vinegars were diverse, and the reason why sediments arise was still unknown. In this thesis, the composition and formation rule of the sediments in SAV were analyzed. This study will provide useful information of the composition of sediments in SAV as well as laied the foundation of understanding the formation mechanism of sediments in traditional Chinese cereal vinegar.By scanning electron microscope (SEM), a preliminary observation of the sediments was conducted. Results showed that there were 3 kinds of substances in sediments:rod-shaped thalli, crystals and amorphous material. Crystals in sediments in SAV are in two shapes. One kind is in regular tetragonal dipyramids, and another is in irregular shape.Through energy dispersive x-ray spectrometry (EDX), microanalyses of two kinds of crystals in sediments were carried out. Results made clear that the two kinds of crystals both were calcium oxalate crystals (CaOxa), of which the regular tetragonal dipyramid one is calcium oxalate dehydrate (COD), while the irregular one is calcium oxalate monohydrate (COM). Besides, starch/ polysaccharides and proteins were proved residing in sediments of SAV by utilizing confocal laser scanning microscopy (CLSM) and fluorescent double-labeling technique. Meanwhile, total sugar, crude fat, total phenols, flavonoids,ligustrazine and five metallic elements (K, Ca, Na, Mg, Fe) as well as nitrogen content were determined. Sugars (ca. 10.9 %), crude fat (ca. 17 %) and nitrogen-contained compounds constitute the main ingredients of the sediments.The formation rule of sediments was analyzed in a seven months' vinegar storage experiment. The result showed that time and temperature were two factors influencing the formation of sediments. Under different storage temperatures, i.e. 4, 15, 25, 35, 45 and 55 ?, the average speed of sediments formation were 0.2322, 0.2557, 0.3355, 0.4187,5.047 and 6.388 g/L/m, respectively. The average speed of sediments formation increased along with temperature rise. It indicated that the formation of sediments was a process influenced by thermodynamics. Meanwhile, several physicochemical indexes were measured, and results showed that sugars, soluble proteins, phenols, colour intensity of the vinegar bulk and particle sizes both of vinegar bulk and sediments were physicochemical indexes which changed a lot. This manifested that complicated physical and chemical reactions were still voyaging. As a whole, particle sizes of the vinegar bulk increased along with the decrease of sugars, soluble proteins and phenols. Sugars, souble proteins and phenols might participate in Maillard reaction and generated insoluble polymeric melanoidins and further (co-)polymerized with particles which already existed in the vinegar bulk resulting in the increase of particle sizes. In storage experiment, particle sizes of the vinegar bulk were all below 1000 nm, while in sediments mostly over 1000 nm. This might indicate that 1000 nm was probably a critical particle size, over which particles begin to settle down. The increase of the particle sizes was the immediate cause, which result in sedimentation of particles. Under different storage temperatures, i.e. 4, 15, 25, 35, 45 and 55 ?, the average speed of decrease of total sugar were 6.552, 6.116, 5.970, 6.004, 6.211 and 7.007 g/L/m, respectively. The average reduction speed of total sugar was correlated with the average speed of sediments formation (r=0.657). What's more, a preliminary analysis on formation mechanism of sediments was made from a colloidal perspective, and a possible mechanism model for elucidating how sediments arising in SAV was proposed. |
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