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牛奶和酸奶中的可滴定酸度

AN-T-132

2020-09

zh

Accurate determination according to DIN 10316, ISO/TS 11869, and IDF/RM 150

可滴定酸度是牛奶和酸奶以及其他发酵乳制品新鲜度的指标。牛奶中测定的可滴定酸度主要是通过牛奶蛋白质和奶盐吸收羟基离子得出的。酸度会随着细菌酸化和酶促脂肪分解而增加。可滴定酸度相当于将 100 克样品滴定到 pH 值为 8.30 时所需的氢氧化钠量。在本应用说明中，展示了一种简便而准确的方法，用于根据 DIN 10316 标准测定牛奶中的可滴定酸度，以及根据 ISO/TS 11869 和 IDF/RM 150 标准测定酸奶中的可滴定酸度。

The titratable acidity gives an indication of the freshness of milk and yogurt as well as other fermented milk products. The determined titratable acidity in milk is mainly given through the absorption of hydroxyl ions by milk proteins and milk salts. The acidity increases with bacterial acidification and with enzymatic lipolysis.

The titratable acidity corresponds to the amount of sodium hydroxide required to titrate 100 g sample to a pH value of 8.30.

In this Application Note, an easy and accurate method to determine the titratable acidity in milk according to DIN 10316 and in yogurt according to ISO/TS 11869 and IDF/RM 150 is demonstrated.

The method is demonstrated for UHT milk and natural yogurt. The samples are prepared according to the standard.

Figure 1. 905 Titrando with tiamo. Example setup for the determination of the titratable acidity in dairy products.

This analysis is performed on a 905 Titrando equipped with a magnetic stirrer and a Porotrode for pH measurement.

Prior to the analysis, the Porotrode must be calibrated in order to ensure accurate results.

A reasonable amount of milk or prepared yogurt sample is used for the titration. An endpoint titration is carried out with standardized sodium hydroxide to a pH value of 8.3.

The analysis demonstrates acceptable and reproducible results. The results are summarized in Table 1. An example titration curve is displayed in Figure 2.

Table 1. Mean titratable acidity of a milk and a yogurt sample determined with a Titrando system (n = 5).
Sample Mean titratable acidity SD(rel) in %
Milk 144.40 mL c(NaOH) = 0.1 mol per L milk 0.28
Yogurt 12.87 mmol NaOH / 100 g 0.17
Figure 2. Example titration curve of the determination of titratable acidity in a dairy product.

After sample preparation, the determination of the titratable acidity can be performed reliably and cost-efficiently by using a Metrohm autotitrator. Fast and precise determination according to DIN 10316, ISO/TS 11869, and IDF/RM 150 is possible.

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Internal reference: AW TI CH1-1156-042014 

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