Utjecaj egzogenih enzima na senzorsku kakvoću tieguanyin oolong čaja ljetne berbe iz kineske pokrajine Anxi

In order to att enuate the bitt er taste and improve the aroma of the summer tieguanyin oolong tea from the Chinese Anxi county, the eff ects of processing treatment with exogenous laccase and α-galactosidase on tea sensory quality and related compounds were investigated. The solutio ns of laccase and/or α-galactosidase were sprayed on the tea leaves before the fi rst drying process. The sensory evaluation results showed that the sensory quality of the tea was signifi cantly enhanced with the enzymatic treatment. The combined application of laccase a t 8.25 and α- galactosidase at 22 U per kg of fresh tea shoots achieved the most satisfying sensory quality. Further analysis of fl avour-related constituents was carried out by HPLC and GC-MS. The HPLC analysis showed that the contents of catechins and total polyphen ols were reduced, compared to the untreated group, by 11.9 and 13.3 % respectively, and the total soluble sugars and water extract content were increased by 19.4 and 6.6 % respectively, aft er the treatment with both enzymes. The decrease of catechins and total polyphenols reduced the bitt erness and astringency of the summer tea, while the increase of total soluble sugars and water extract content improved the sweetness and mellow taste. The aromatic compound data from GC-MS showed that the total essential oil content in these tea samples co-treated with laccase and α-galactos idase increased significantly, in which aldehydes, alcohols, esters and alkenes increased by 23.28, 37.05, 20.10 and 38.99 %, respectively. Our data suggest that the exogenous enzymatic treatment can enhance the summer oolong tea quality, especially its taste and aroma.U radu je ispitan utjecaj tretiranja mladica tieguanyin oolong čaja ljetne berbe iz kineske pokrajine Anxi egzogenim enzimima, i to lakazom i α-galaktozidazom, na ublažavanje gorkog okusa te poboljšanje arome i senzorske kakvoće čaja. Prije početka sušenja, mladice su čaja bile prskane otopinama lakaze i/ili α-galaktozidaze. Rezultati senzorske analize pokazuju da su enzimskom obradom bitno poboljšana organoleptička svojstva čaja. Najbolji su rezultati postignuti tretiranjem mladica otopinom 8,25 U lakaze i 22 U α-galaktozidaze po kilogramu svježih mladica. Pomoću metoda HPLC i GC-MS ispitani su sastojci arome, pri čemu je metodom HPLC utvrđeno da se nakon obrade enzimima udjel katehina smanjio za 11,9 %, a ukupnih polifenola za 13,3 %, te povećao udjel ukupnih topljivih šećera za 19,4 % i vodenog ekstrakta za 6,6 %, u usporedbi s netretiranim uzorkom. Smanjenjem udjela katehina i ukupnih polifenola smanjila se gorčina i trpkost čaja, a povećanjem udjela ukupnih topljivih šećera i vodenog ekstrakta dobiven je čaj blagog i slatkog okusa. Rezultati analize aromatskih spojeva metodom GC-MS pokazuju da se ukupni udjel eteričnih ulja u uzorcima čaja tretiranim s oba enzima bitno povećao, i to aldehida za 23,28 %, alkohola za 37,05 %, estera za 20,10 % i alkena za 38,99 %. Dobiveni podaci upućuju na zaključak da se obradom oolong čaja ljetne berbe egzogenim enzimima može poboljšati okus i aroma čaja

Bet hedging in the underworld

Under starvation conditions, the soil bacterium Sinorhizobium meliloti divides into two types of daughter cell: one suited to short-term and the other to long-term starvation