612. Steam distillation of taints from cream: II. Investigations on commercial equipment with use of diacetyl and acetoin as reference substances

Steam distillation of taints from cream: IV. Vapour/liquid equilibrium relationships for mesityl oxide and some α-diketones as possible reference substances

1. Measurements, by means of a continuous vaporization equilibrium still, of vapour/liquid equilibrium relationships in the steam distillation of dilute aqueous solutions showed that for mesityl oxide the relationship was linear, equilibrium coefficient (CV/CL)= 74.

2. For acetylpropionyl it was linear over the concentration range l–10 p.p.m. in the liquid, CV/CL=51, and above a concentration of 20 p.p.m. it was again approximately linear. At 20 and 50 p.p.m. in the liquid the values found for CV/CL were 34 and 21·5 respectively.

3. For acetyl-iso-butyryl it was not linear even at very low concentrations, of the order of 1–3 p.p.m. in the liquid, but there was an approach to linearity at concentrations 0–1 p.p.m., CV/CL=240. At concentrations above 1 p.p.m. in the liquid there was a steady fall in the value for the equilibrium coefficient.

4. For acetylvaleryl it was curvilinear even over the concentration range 0·1–4·0 p.p.m. in the liquid. At 0·5–1·0 p.p.m. in the liquid the equilibrium coefficient was of the order of 240. Above a concentration of 4 p.p.m. in the liquid the relationship was linear.

5. For acetylcaproyl it was approximately linear only over the concentration 0·1–0·4 p.p.m. in the liquid, CV/CL=180. At 4 and 8 p.p.m. in the liquid the coefficients were 90 and 70 respectively.

6. For acetylbenzoyl it was curvilinear at low concentrations, i.e. 0·1–0·5 p.p.m. in the liquid, CV/CL=30 decreasing to 16. Above this concentration there was a gradual fall in the equilibrium coefficient to 11·5 at 70 p.p.m. in the liquid.

7. Of the substances investigated only diacetyl and acetylpropionyl and, within limits, acetylbenzoyl were considered to be of suitable properties for use as reference substances in detailed investigations on cream deodorization equipment.

687. Changes in size of fat globules in cream during Vacreator treatment

The size distribution of fat globules was determined microscopically in cream samples taken from different parts of the Vacreator during treatment of cream.

A considerable increase in numbers of small globules (splitting) was found in samples which had passed the equilibrium valve. Smaller increases took place in the pasteurizing chamber and in the extractor pump. Increase in numbers of large globules (clumping) occurred in the cooler section.

Splitting of globules could be reduced: in the pasteurizer by reducing velocity of incoming steam; at the equilibrium valve by reducing the vacuum drop across the valve or by introducing part of the steam at the infuser instead of into the pasteurizer.

It is concluded that splitting of globules in the Vacreator is due to a homogenizing effect where steam and cream travel at a high velocity. Flash-boiling causes clumping but not splitting of globules. These conclusions should apply to any equipment for pasteurization or deodorization of cream with direct steam.

The thanks of the author are due to Mr J. Singleton (Superintendent) and Mr B. Le Heron (Buttermaker) of the Institute factory for arranging and carrying out Vacreator treatments of cream, to Dr F. H. McDowall for helpful advice and criticism and to Mrs R. P. Haverkamp for assistance in measuring fat globules.

669. Steam distillation of taints from cream: III. Factors affecting rate of removal of the reference substances, diacetyl and acetoin

1. The vapour/liquid equilibrium coefficient for diacetyl in 35–40% cream has been found to be of the order of 26–28, compared with 39·3 for water. In a 5% aqueous solution of lactose, equivalent to that present in milk and in cream serum, the coefficient was 30. The depression of the equilibrium coefficient by lactose in solution was shown to be independent of the concentration of diacetyl present in the liquid at time of partition, over the range 1–65 p.p.m.

2. The slower rate of removal of diacetyl from cream, per unit weight of steam condensed as compared with its removal from water, was observed to be due mainly to this depressing effect of lactose on the equilibrium coefficient; but there was some evidence that delay in re-establishment of the solubility partition equilibrium as between butterfat and cream serum also contributed to the lowering of the equilibrium coefficient for diacetyl in cream as measured in the laboratory continuous vaporization equilibrium still.

3. Sodium chloride in the solution caused a rise in the equilibrium coefficient for diacetyl from the value of 39·3 for water to about 69 for a 10% salt solution and 82 for a 20% salt solution.

4. Lactose had no effect on the equilibrium coefficient for acetoin, but salt caused a rise from 1·29 for water to approximately 1·75 for a 10% salt solution.

5. The possible effect of lactose on the effectiveness of steam in cream deodorization equipment is referred to.

Steam distillation of taints from cream: V. Vapour/liquid equilibrium relationships for some α-diketones in lactose solution

1. The effect of 4·5% lactose in solution on the vapour/liquid equilibrium relationship for acetylpropionyl, acetyl-iso-butyryl, acetylvaleryl, acetylcaproyl and acetylbenzoyl has been investigated.

2. There was no appreciable effect on the relationship for acetylpropionyl and acetylbenzoyl.

3. For acetyl-iso-butyryl there was a lowering of the coefficient at low concentration of diketone in the liquid, but at concentrations above 4 p.p.m. there was no appreciable effect.

4. For acetylvaleryl at low concentrations in the liquid the coefficient was lowered, and at concentrations above 3·0 p.p.m. in the liquid it was increased.

5. For acetylcaproyl the coefficient was lowered by presence of 4·5% lactose in the solution.

6. Change in concentration of lactose over the range 0·5—10% had little effect on the vapour/liquid equilibrium coefficient for acetylpropionyl and acetylbenzoyl, but it caused a progressively increased reduction in the coefficient for acetyl-iso-butyryl, acetylvaleryl and acetylcaproyl.

Steam distillation of taints from cream: VI. Butterfat/lactose-solution distribution coefficients of some reference substances

1. Coefficients of distribution for acetoin, diacetyl and acetylpropionyl between butterfat and skim-milk were measured over a range of temperatures up to 190° F. by passing preheated milk containing the reference substance through an hermetic cream separator and analysing the cream and skim-milk obtained.

2. The coefficients increased with rise in temperature, and the relationship between change in coefficient and change in temperature was linear for all three substances.

3. Coefficients of distribution for acetyl-iso-butyryl, acetylvaleryl, acetylcaproyl and acetylbenzoyl between butterfat and 4·5% lactose solution were measured at 40° and 60° C. by direct separation after equilibration, followed by estimation of the diketone in the lactose solution.

4. Coefficients of distribution at 100° C., obtained by linear extrapolation from these results, were: acetoin, 0·255; diacetyl, 1·27; acetylpropionyl, 5·9; acetyl-iso-butyryl, 20; acetylvaleryl, 23; acetylcaproyl, 152; acetylbenzoyl, 48.

5. The coefficients of distribution for diacetyl and acetylpropionyl between butterfat and 4·5% lactose solution were not affected by change in concentration of the diketone in the lactose solution.