石灰法、亚硫酸法和碳酸法清净对蔗汁脱色(上)

Removal of Colour in Sugar Cane Juice Clarification by Defecation, Sulfitation and Carbonation (Part Ⅰ)

色值是糖品最重要的特性,但在蔗汁清净中,通常不把脱色看作主要目标。根据实验结果,所有的常规清净方法都有显著的脱色潜力,甚至比工业实践中所意识到的更高。测试了4种主要的清净方法:热汁加灰石灰法、亚硫酸法、单碳酸法和双碳酸法,并研究了各种清汁的色值特性。碳酸法在甘蔗糖业中的应用不是很广泛,但硫磺价格的周期性上涨、糖质量问题和环境问题,都促使人们设法考虑用发酵车间免费的CO2替代或补充SO2。研究了粗汁和清汁间的相对脱色率,石灰法、亚硫酸法、单碳酸法和双碳酸法的平均脱色率分别为35%、47%、44%、74%。检测了影响石灰法清汁色值的几个因素,即:沉降停留时间和温度、蔗渣和滤泥含量、磷酸和蛋白质添加量的影响。加灰量低于1 kgCaO/t蔗(石灰法、亚硫酸法、单碳酸法)情况下,除了新生成的磷酸钙沉淀对色素的吸附外,很大一部分脱色效果来自于受热凝结的甘蔗蛋白的吸附。在常规清净方法中,用于吸附色素的磷酸钙沉淀是过量的。亚硫酸法和单碳酸法的脱色效果接近,但单碳酸法处理得到的清汁和糖浆的热稳定性明显较差,需要进一步研究。

Colour is the most important commercial sugar attribute but in juice clarification its removal is usually not considered among primary objectives. However, based on results presented, all standard clarification procedures have the potential for significantly higher removal of colour than is realised in the industrial practice. Four principal juice clarification procedures, viz. defecation by hot liming, sulfitation, carbonation and double-carbonation were tested and various aspects of colour behaviour investigated. Carbonation is not widely used in the cane sugar industry, but periodic spikes in sulfur prices, sugar quality issues and environmental concerns have stimulated efforts to consider replacing or supplementing sulfur dioxide with carbon dioxide that may be available cost-free from the fermentation plant. The colour removal, viz. the relative difference between colour of raw and clarified juice, obtained in our tests was on average 35, 47, 44 and 74% for defecation, sulfitation, single-carbonation and modified double-carbonation, respectively. Several factors affecting clarified juice colour in hot liming were tested, viz. the time and temperature during settling; bagacillo and soil content,and phosphate and protein addition. At low lime dose, below about 1 kg CaO/tonne cane （defecation, sulfitation and carbonation）, significant portion of colour removal results from adsorption on the heat-coagulated cane protein, in addition to its capture by the nascent calcium phosphate precipitate. However, the adsorptive capacity of the precipitate for cane colorants appears only partially exhausted in the normal procedure. Although the decolourisation effects of sulfitation and carbonation were found to be about equal, the apparently lower thermal stability of clarified juice and syrup produced by carbonation may require further study.