Food Science and Technology, School of Chemical Engineering, The University of New South Wales, Sydney, New South Wales, Australia.
Yeast. 2023 Sep;40(9):425-436. doi: 10.1002/yea.3888. Epub 2023 Jul 19.
During wet fermentation, mucilage layers in coffee cherries must be removed completely. To explain mucilage degradation, several controversial hypotheses have been proposed. The aim of this work was to improve our understanding of the kinetics of mucilage breakdown. Pulped coffee beans were wet fermented with seven different treatments for 36 h. Endogenous bacteria and yeasts are selectively suppressed, and pectinases or lactic acid are added. They also involve maintaining the beans at pH 7 throughout fermentation and using spontaneous fermentation without additives as a control. During spontaneous fermentation, yeast and lactic acid bacteria were detected and significantly increased to 5.5 log colony-forming units (CFU)/mL and 5.2 log CFU/mL, respectively. In the first 12 h of fermentation, there was a significant degree of endogenous pectinolytic activity, which resulted in partly destroyed beans in the absence of microorganisms. By adding pectinase and lactic acid to the fermentation mass, the breakdown process was accelerated in less than 8 h. When yeast was present throughout the fermentation, complete degradation was achieved. Bacteria played no critical role in the degradation. Klebsiella pneumoniae and Erwinia soli were found in a lower population and showed weaker pectinolytic activities compared to Hanseniaspora uvarum and Pichia kudriavzevii. During wet fermentation, mucilage degradation appears to be mediated by endogenous enzymes at the early stage, whereas microbial contributions, mainly yeasts, occur subsequently. H. uvarum and P. kudriavzevii may be promising candidates to be tested in future studies as coffee starter cultures to better control the mucilage degradation process.
在湿法发酵过程中，咖啡樱桃的黏液层必须完全去除。为了解释黏液降解，提出了几个有争议的假设。本工作的目的是提高对黏液分解动力学的理解。将去皮咖啡豆用七种不同的处理方法湿发酵 36 小时。内源性细菌和酵母被选择性抑制，并添加果胶酶或乳酸。它们还涉及在整个发酵过程中保持豆的 pH 值为 7 并使用无添加剂的自发发酵作为对照。在自发发酵过程中，检测到酵母和乳酸菌，并分别显著增加到 5.5 log 菌落形成单位（CFU）/mL 和 5.2 log CFU/mL。在发酵的前 12 小时内，存在显著程度的内源性果胶酶活性，导致在没有微生物的情况下部分破坏豆。通过向发酵物中添加果胶酶和乳酸，在不到 8 小时的时间内加速了分解过程。当酵母存在于整个发酵过程中时，完全降解就可以实现。细菌在降解过程中没有起到关键作用。肺炎克雷伯菌和成团泛菌的数量较少，与汉逊酵母和毕赤酵母相比，果胶酶活性较弱。在湿法发酵过程中，黏液降解似乎在早期阶段由内源性酶介导，而微生物的贡献，主要是酵母，随后发生。汉逊酵母和毕赤酵母可能是有前途的候选菌株，可在未来的研究中作为咖啡启动培养物进行测试，以更好地控制黏液降解过程。
