熱加工與高壓處理對莓類果汁加工安全性與 花青素降解之研究

Effect of heat and high pressure treatments on the safety and anthocyanins retention in berry juice

許馨云(Hsin-Yun Hsu)

指導教授 ： 吳瑞碧

國立臺灣大學/生物資源暨農學院/食品科技研究所/博士(2013年)

https://doi.org/10.6342/NTU.2013.01503

摘要

食品加工的主要目的之一為減少或消除病原性微生物，維持產品的機能活性與感官特性，同時延長產品的貨架期。食品加工操作多利用熱能，例如：巴斯德殺菌(Pasteurization)、殺菁(Blanching)、乾燥(Drying)等；但在高於環境溫度時，會引起明顯的品質屬性降低，包括：風味、質地、顏色、熱敏性營養成分及機能活性等。
富含花青素的新鮮莓果(例如:桑椹與草莓)，不但具有鮮豔色澤吸引消費者之青睞同時也提供抗氧化等機能特性，為當今廣為食用的水果。本研究擬以花青素為指標，利用一快速升降溫裝置(fast-heating fast-cooling model system, FHFC system)，模擬熱交換器系統加工過程，針對富含花青素之桑椹果汁(MJ)其總花青素(TAC)熱降解情形與其顏色變化、抗氧化活性表現進行分析。新鮮桑椹經過適當的加工處理後得到澄清果汁，利用FHFC裝置進行不同溫度時間的熱處理(70-130oC/0-960 min)後，分析其總花青素含量及顏色。桑椹果汁之總花青素、顏色值(a*, L*×a*×b*)、最大波長吸收值(A514) 之降解屬一級反應動力學，且隨著溫度的提升，裂解速率顯著增加(p<0.05)。其活化能分別為108.7、89.2、82.8及88.1kJ/mol。相較於其他莓果類花青素，桑椹花青素具有較佳的熱穩定性。花青素之含量與A514，顏色值(a*, L*×a*×b*)彼此間具高相關性。建議可以A514之檢測來快速推估或線上監測總花青素存留量。
富含花青素之莓果一但受到病原菌(如Escherichia coli O157:H7)汙染後，必須進行適當的殺菌處理才能提供給消費者食用。本論文之第二部分，是以草莓泥(SP)熱殺菌條件參數之建立與高壓殺菌(HPP)應用之安全性評估為主。利用志賀毒性大腸桿菌(Shiga toxin-producing E. coli, STEC)為指標，同時監測樣品花青素含量與產品顏色變化，以及儲存期間黴菌與酵母菌生長之情形。新鮮草莓泥樣品(糖度8oBrix或調整至20及40 oBrix)，接菌後，以50、52、54、57.5、60及62.5°C進行熱致死條件評估。結果顯示，殺菌值(D-value)會受到溫度的提升而顯著降低，然而含糖量的提高反而會提高其值，同時對花青素存留與顏色有保護作用。經計算後，分別得到平均殺菌值為909.1、454.6、 212.8、46.1及20.2秒，z值為5.9°C。
另一部分為高壓殺菌(HPP)致死病原菌之可行性與安全性評估。新鮮草莓泥經過適當接種後，以150、250、350、450、550及650 MPa壓力分別進行5、15及30分鐘的處理。結果顯示: 以壓力350MPa進行5分鐘的處理條件能顯著降低6-log CFU/g之病原菌。同時透過電子式顯微鏡(SEM)的結果清楚地提供高壓處理對病原菌所造成之物理性且不可逆破壞的證據。結果得知，HPP處理對於熱敏感性產品(如富含花青素莓果)能提供較佳的加工後產品品質，同時有助於控制產品安全性。

關鍵字

熱加工處理 ； 高壓處理 ； 花青素 ； 志賀毒性大腸桿菌 ； 桑椹 ； 草莓

並列摘要

Food processing, a method used to eliminate pathogen, maintain sensory and bioactivity characteristics and extend the shelf-life of products. When the processing temperature is higher than the ambient temperature, it will lead food products to undesired quality, including heat-sensitive nutrients lossed, color changed. Fresh berries, mulberry and strawberry contain abundant anthocyanins with attractive brilliant red color and provide health benefits.
This study was aimed to simulate the thermal processing of Morus alba L. mulberry juice (MJ) and to evaluate the kinetic parameters for the retention of total anthocyanins content (TAC), the relationship between the changes in color and TAC, and to search for a convenient on-line indicator for TAC using a fast-heating fast-cooling model (FHFC) system. Fresh mulberry was homogenized, de-pectinized, blanched, and filtered to obtain the clear juice. The MJ was then processed in the FHFC system at various holding conditions (70-130oC/0-960 min). Results indicate that the TAC, CIE a* value, total color index (L*×a*×b*), and the maximum absorbance which occurs at 514nm (A514) all decrease in time and temperature-dependent manners (p<0.05) following first-order reaction kinetics. The activation energies (Ea) were 108.7, 89.2, 82.8, and 88.1kJ/mol, respectively. There are good linear correlations among A514, a*, L*×a*×b*, and TAC. We propose to take A514, which can easily be assessed using a spectrophotometer with digital output, as an indicator for the on-line estimation of TAC in the thermal processing of MJ.
Raw whole strawberries, if contaminated with pathogens such as Escherichia coli O157:H7, must be pasteurized prior to consumption. The objective of another part of this dissertation was to investigate the thermal and high pressure processing (HPP) inactivation of Shiga toxin-producing E. coli (STEC) in strawberry puree (SP), and evaluate the changes of anthocyanins and color, and the survival of yeasts and molds (YM) after processing. Inoculated fresh SP, with or without added sugar (20 and 40 oBrix), was heated at 50, 52, 54, 57.5, 60, and 62.5°C to determine the thermal resistance of E. coli O157:H7, survival of YM, degradation of anthocyanins, and changes in browning index. The average D-values of E. coli O157:H7 in raw SP were 909.1, 454.6, 212.8, 46.1, and 20.2 s at 50, 52, 54, 57.5, and 60°C, respectively, with a z-value of 5.9°C. While linearly decreasing with temperature, the log D values of E. coli O157:H7 increased slightly with sugar concentration. The log degradation rates of anthocyanins increased linearly with temperature, but decreased slightly with sugar concentrations. These results suggest that sugar may provide some protection to both E. coli O157: H7 and anthocyanins in SP.
The other objective of this part of dissertation was to explore the potential application of HPP treatment to reduce or eliminate STECs in SP. Inoculated SP was vacuum sealed, and then pressure-treated at 150, 250, 350, 450, 550, and 650 MPa for 5, 15, and 30 min. HPP treatment, at 350 MPa for ≥ 5 min, significantly reduced STECs in SP by 6-log CFU/g from the initial cell population of ca. 8-log CFU/g. The scanning electron microscopy (SEM) images clearly provided the physical evidence that high pressure may kill the cells and the damage may be irreversible. The results demonstrated that the HPP treatments can be potentially used to control STECs in heat sensitive products.

並列關鍵字

Thermal processing ； High pressure processing ； Anthocyanins ； Shiga toxin-producing Escherichia coli ； Mulberry ； Strawberry

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