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ข้อคิดเห็นจากผู้ทรงคุณวุฒิจะแสดงในกรอบสีเขียว ส่วนข้อคิดเห็นหรือความเห็นจากผู้อื่นจะแสดงในกรอบปกติ
ข้อคิดเห็นที่
1: The pH value of a milk solution or milk product represents the present (true) accidity. Normal milk is a slightly acid solution with a pH falling between 6.5 and 6.7 with 6.6 the most usual value. ( At 25"C ; The pH is checked with a pH-meter ) Titratable acidity Acidity can also be expressed as the titirable. The titrable acidity of milk is the amount of a hydroxyl ion (OH-) solution of a given strength needed to increase the pH of a given amount of milk to a pH of about 8.4, the pH at which the normally used indicator, phenolphtalein, changes colour from colourless to pink. What this test really does is to find out how much alkali is needed to change the pH from 6.0 to 8.4. If milk sours on account of bacterial activity, an increased quantity of alkali is required and so the acidity or titration value of the milk increas- es . The titratable acidity can be expressed in various values basically as a result of the strength of the sodium hydroxide (NaOH) needed at titration, °SH = Soxhlet Henkel degrees, obtained by titrating 100 ml of milk with N/4 NaOH , using phenolphtalein as the indicator. Normal milks give values about 7. This method is mostly used in Central Europe. °Th = Therner degrees, obtained by titrating 100 ml of milk, thinned with 2 parks of distilled water, with N/l0 NaOH, using phenolphtalein as the indicator. Normal milks give values about 17. Mostly used in Sweden and the CIS, °D = Dornic degrees, obtained by titrating 100 ml of milk with N/9 NaOH, using phenolphtalein as the indicator. Normal milks give values about 15. Mostly used in the Netherlands and France. % l.a. = per cent lactic acid, obtained as °D with the result divided by 100. Frequently used in the UK, USA, Canada, Australia and New Zealand In table 2.9 the various expressions for the titratable acidity are combined. Table 2.9 Acidity is often expressed in one of these ways °SH 1 0.4 4 / 9 °Th 2.5 1 10 / 9 °D 2.25 0.9 1 %I.a. 0.0225 0.009 0.01 Example: 1.7 ml of N/10 NaOH are required for titiration of a 10ml sample of milk 10 × 1.7 = 17ml would therefore be needed for 100mlm and the acidity of the milk is consequently 17°Th. โดย: Multi-Minded [21 ม.ค. 2553 13:39] |
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2: http://jds.fass.org/cgi/content/full/89/3/859 โดย: Multi-Minded [21 ม.ค. 2553 13:45] |
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