IMPROVEMENTS IN FRYING TECHNOLOGY

Abstract

A method for preserving cooking oil comprises contacting the oil with oil-permeable cementious material in the form of either stand-alone blocks, pellets, granules, or balls and which has been hydraulically hardened from a paste comprising (a) >50 wt % of (i) white OPC clinker, (ii) white OPC or (iii) a mixture of white OPC clinker and white OPC, and (b) optionally further ingredients selected from silica, titania, lime, calcium sulphate, hydrated alumina, natural feldspars, diatomaceous earth, Na and Ca forms of natural and synthetic zeolites, clays, pillared clays, activated clays/earths, silicate minerals selected from calcium silicate, magnesium silicate, aluminium silicate, agalmatolite, amphiboles, attapulgite, granite porphyry, kaolinite, porphyry, rhyolite, talc and wollastonite, wherein the porosity of the cementious material is 30-55%. The oil-permeable cementious material has during manufacture been subjected to prolonged drying at elevated temperatures so as to reduce the amount of foaming occurring in the oil during treatment with the said cementious material.

Claims

1. A method for preserving cooking oil which comprises contacting the oil with oil-permeable cementious material in the form of either stand-alone blocks, pellets, granules, or balls and which has been hydraulically hardened from a paste comprising:— (a) >50 wt % of (i) white OPC clinker, (ii) white OPC or (iii) a mixture of white OPC clinker and white OPC, and (b) optionally further ingredients selected from silica, titania, lime, calcium sulphate, hydrated alumina, natural feldspars, diatomaceous earth, Na and Ca forms of natural and synthetic zeolites, clays, pillared clays, activated clays/earths, silicate minerals selected from calcium silicate, magnesium silicate, aluminium silicate, agalmatolite, amphiboles, attapulgite, granite porphyry, kaolinite, porphyry, rhyolite, talc and wollastonite, wherein the porosity of the cementious material is 30-55%, characterised in that the oil-permeable cementious material has during manufacture being subjected to prolonged drying at elevated temperatures so as to reduce the amount of foaming occurring in the oil during treatment with the said cementious material.

2. The method of claim 1, wherein the paste also includes at least 5% by weight of microsilica.

3. The method of claim 1, wherein the paste also includes anhydrite.

4. The method of claim 1, wherein the paste also includes a non-toxic air entraining agent.

5. The method of claim 1, wherein the drying takes place for at least 18 hours.

6. The method of claim 1, wherein the drying takes place for at least 24 hours.

7. The method of claim 1, wherein the drying takes place at at least 180° C.

8. The method of claim 1, wherein the drying takes place at at least 200° C.

9. The method of claim 1, wherein the drying takes place at at least 230° C.

10. A product for prolonging the life of cooking oil, being an oil-permeable cementious material in the form of either stand-alone blocks, pellets, granules, or balls and which has been hydraulically hardened from a paste comprising:— (a) >50 wt % of (i) white OPC clinker, (ii) white OPC or (iii) a mixture of white OPC clinker and white OPC, and (b) optionally further ingredients selected from silica, titania, lime, calcium sulphate, hydrated alumina, natural feldspars, diatomaceous earth, Na and Ca forms of natural and synthetic zeolites, clays, pillared clays, activated clays/earths, silicate minerals selected from calcium silicate, magnesium silicate, aluminium silicate, agalmatolite, amphiboles, attapulgite, granite porphyry, kaolinite, porphyry, rhyolite, talc and wollastonite, wherein the porosity of the cementious material is 30-55%, characterised in that the oil-permeable cementious material has during manufacture being subjected to prolonged drying at elevated temperatures so as to reduce the amount of foaming occurring in the oil during treatment with the said cementious material

11. The product of claim 10, wherein the paste also includes at least 5% by weight of microsilica.

12. The products of claim 10, wherein the paste also includes wherein the paste also includes anhydrite.

13. The products of claim 10, wherein the paste also includes a non-toxic air entraining agent.

14. The products of claim 10, wherein the drying takes place for at least 18 hours.

15. The products of claim 10, wherein the drying takes place for at least 24 hours.

16. The products of claim 10, wherein the drying takes place at at least 180° C.

17. The products of claim 10, wherein the drying takes place at at least 200° C.

18. The products of claim 10, wherein the drying takes place at least 230° C.

Description

DESCRIPTION OF PREFERRED EMBODIMENTS

Fryers

[0058] The invention is applicable to the in situ treatment of cooking oil in deep fat fryers of the type used in restaurants, fast food outlets or in pubs which typically have a capacity for approximately 5-40 litres. It is also applicable to domestic deep fat fryers and for use in larger industrial fryers.

Materials

[0059] The treatment materials that are suitable for use in embodiments of this invention are those cementious materials that are disclosed in the specifications of the BBM Patents, which are incorporated herein in their entirety by reference. Particularly suitable treatment materials are cementious materials made substantially from pastes comprising (a) >50 wt % of (i) white OPC clinker or (ii) white OPC or (iii) a mixture of white OPC clinker and white OPC, and (b) optionally further ingredients selected from silica, titania, lime, calcium sulphate, hydrated alumina, natural feldspars, diatomaceous earth, Na and Ca forms of natural and synthetic zeolites, clays, pillared clays, activated clays/earths, silicate minerals selected from calcium silicate, magnesium silicate, aluminium silicate, agalmatolite, amphiboles, attapulgite, granite porphyry, kaolinite, porphyry, rhyolite, talc and wollastonite, wherein the porosity of the cementious material is 30-55%.

[0060] Such pastes advantageously also contain minor amounts of microsilica/silica fume and suitable air entraining agents, as hereinafter described.

[0061] Where clinker alone is used rather than a mixture of OPC and clinker then calcium sulphate (anhydrite) must be added to prevent flash setting.

[0062] Treatment media were made with Alborg white cement clinker and Alborg White OPC. Alborg white clinker is made using an extremely pure limestone originating from a marine deposit which is now located in Denmark and was obtained from Aalborg Portland A/S—Denmark, Aalborg Portland A/S, Rørdalsvej 44, P.O. Box 165, 9100 Aalborg, Denmark.

[0063] The unmilled clinker was obtained from Hanson Cement, Ketton Works Ketton, Stamford, Lincolnshire.

[0064] As an alternative to using a mixture of OPC and clinker, the man skilled in the art will readily appreciate that it is possible to make the treatment medium of the invention using either OPC alone or clinker alone, OPC alone being preferred because of its ready availability and ease of handling compared to clinker. Where clinker alone is used in place of a mixture of OPC and clinker then calcium sulphate (anhydrite) must be added to prevent flash setting.

[0065] A typical composition of the Alborg clinker used is:—

SiO.SUB.2 .25.0%

[0066] Al.sub.2O.sub.3 2.00%
Fe.sub.2O.sub.3 0.30%

CaO 69.0

[0067] This gives a calculated Bogue composition as follows:—

C.SUB.3.S 65.0%

C.SUB.2.S 21.0%

C.SUB.3.A 5.0%

C.SUB.4.AF 1.0%

CaSO.SUB.4 .0%

[0068] The equivalent typical figures for the OPC used in this experiment were:—

SO.SUB.3 .2.03%

SiO.SUB.2 .24.4%

[0069] A.sub.12O.sub.3 1.97%
Fe.sub.2O.sub.3 0.34%

CaO 68.6%

MgO 0.58%

Cl 0.01%

TiO.SUB.2 .0.09%

[0070] P.sub.2O.sub.5 0.30%

K.SUB.2.O 0.16%

Na.SUB.2.O 0.19%

[0071] Thus giving a calculated Bogue composition (corrected to take into account a free lime content of about 3%):

C.SUB.3.S 66.04%

C.SUB.2.S 20.1%

C.SUB.3.A 4.64%

C.SUB.4.AF 1.04%

CaSO.SUB.4 .3.45%

[0072] Importantly the clinker has a very low free iron content which is important as iron is a powerful pro-oxidant trace metal, (see for example Sonntag 1979 in Bailey's industrial Oil and fat Products, New York, John Wiley and Sons, Vol 1. pp 152).

[0073] The clinker was milled by an external ball-miller to a “ready-to-use” grain-size of nominally 14.5 μm, with the particle size distribution being such that the d50 was 13.33 μm±4.7%, which was approximately the same size as the cement used. Once milled the clinker was kept in a dry sealed plastic container to prevent clumping, until use.

[0074] Both the clinker and the cement were fine sieved immediately prior to mixing to remove any large clumps before the addition of the water. The addition of deionised water is preferred but this is not essential to a satisfactory embodiment of the invention disclosed herein.

[0075] The mix to make the filters comprised three parts of clinker to one part of OPC as well as relatively minor amounts of microsilica (12% by weight of the paste) and a small amount of Microair 119, an air entraining agent manufactured by BASF, added in accordance with user instructions.

[0076] For many years entrained air has been deliberately incorporated into concrete and cement mixtures in parts of the world which experience freezing so as to reduce the damage caused by repeated cycles of freezing and thawing. Chemical additives, known as air entraining agents, are used to produce a stable system of discrete air voids, which are typically extremely small being between 10 μm and 1 mm. There are normally more than 1 million such bubbles in one cubic inch of treated paste or more than 60,000 per cubic centimetre. The entrained air void system in cement can be viewed and determined from the examination of a cut and polished section of a hardened cement sample, using microscopic techniques in accordance with ASTM C457 (standard test method for microscopical determination parameters of the air void system in hardened concrete).

[0077] Such air voids provide empty spaces within the cement or concrete and are known to act as storage sites for freezing water moving in the capillary pores, thereby relieving the pressure generated during freezing and preventing damage to the cement or concrete. The addition of relatively small amounts of air entraining agents to mixtures of the type used to make the filters of the type described in the BBM Patents produces very much more porous filters, which absorb very considerably much more free fatty acids and aldehydes than filters without such air entraining agents. There are a number of well-known types of air entraining agents.

[0078] Typically these are surfactants and include for example wood derived acid salts, wood rosin, tall oil, vegetable oil acid salts such as the alkanolamine salt of coconut oil, synthetic detergents such as alkyl-aryle sulfonates and sulfates such as dodecylbenzenesulfonate. The surfactant used in the invention disclosed herein must be non-toxic. The man skilled in the art will readily be able to identify numerous such non-toxic air entraining agents suitable for use in the invention herein described.

[0079] Thorough mixing of the clinker, the OPC, the air entraining agent and the microsilica, using an industrial mixer took place and then sufficient water was added to give a good paste in accordance with the following mix design:—

TABLE-US-00004 WHITE CEMENT Kg 0.900 CLINKER Kg 2.700 DEIONISED WATER Kg 1.800 ANHYDRITE Kg 0.054 MICROSILICA Kg 0.400 Microair 119 ml 24.000 Dry Total 4.05

[0080] Assuming about 10% of the mix was wasted in the mixer and in the moulds this 4.05 kg of mix would typically produce about 15 treatment blocks, each with a weight before drying of 240 gms.

[0081] The paste was then placed into moulds, of the type depicted in FIGS. 1 to 4 of WO/2013/121206 and as further described in that patent application and left to cure for 24 hours at room temperature in curing chambers (essentially closed boxes) where the relative humidity was kept near 100%. After 24 hours the paste was found to be fully set and capable of easy demoulding by manipulation of the flexible sidewalls of the moulds.

[0082] The dimensions of the filters were approximately 15 cm×2 cm×9 cm with 30 holes each with a diameter of approximately 0.5 cm: (these figures ignore slight tapering of the filter to facilitate extraction from the mould).

Drying

[0083] Thereafter the demoulded treatment blocks were dried in an industrial oven for at least 18 hours and more preferably for at least 24 hours at a temperature of at least 200° C. and most preferably 230° C. This prolonged drying at an elevated temperature has surprisingly been found to be essential to produce a filter that does not foam in use. The drying at such elevated temperatures for at least 18 hours and more preferably for at least 24 hours was such so that the weight of the filters did not appreciably further reduce after 18 hours no matter how much longer the filters were dried at this temperature and typical figures are given below in table 4. The weights shown are average weights for ten treatment blocks.

TABLE-US-00005 Start Weight Temperature Time End weight 235 gm 130° C.  6 hours 226 gm 235 gm 130° C. 12 hours 220 gm 234 gm 130° C. 24 hours 217 gm .sup. 236 gms 230° C.  6 hours 226 gm 233 gm 230° C. 12 hours 218 gm 233 gm 230° C. 18 hours 212 gm 235 gm 230° C. 24 hours 210 gm 234 gm 230° C. 48 hours 209 gm 236 gm 230° C. 72 hours 211 gm

[0084] This prolonged drying at elevated temperatures was found to be an essential step to reduce foaming as further described herein below. Without wishing to be bound by any theory, it is believed that the prolonged drying at these temperatures evaporated off water in the pores in the cement and further led to the losses of some water of hydration within the cement minerals. Such water emanating from the cementious material can be expected to contain substantial amounts of dissolved calcium hydroxide and calcium ions, which on coming into contact with hot cooking oil and breakdown products such as fatty acids are highly likely to make calcium fatty acid salts (soaps), thus leading to the formation of an impermeable layer on top of the oil which causes foaming during cooking.

[0085] The filters after drying were left in the oven to cool down and once they were sufficiently cool they were taken out of the oven and immediately individually wrapped with impermeable to water plastics packaging material to prevent any water absorption by them.

Porosity

[0086] The porosity of hardened cement paste is discussed e.g. by Alford et al. in their article entitled “An assessment of porosity and pore sizes in hardened cement pastes”, J. Materials Sci., 16, (1981) 3105-3114. The porosity of a cementious article can be estimated by firstly weighing the article after it has been dried in an industrial oven (to give weight A) and then immersing it in water at room temperature until the article is fully saturated with water and then weighing it fully saturated (weight B). The total weight of the water taken up is then weight B minus weight A, which when multiplied by the density of the cement/density of water gives a figure which as a percentage of weight A represents the porosity of the filter.

[0087] The filters made for the purposes of this example had a porosity determined in accordance with the above described method of between 45 to 50%.

Frying Trials

[0088] Forty sets of trial frying runs were undertaken without any foraminous enclosures being used. 20 of the frying trials were carried out in an 18 L electric fryer and 20 of them were carried out in a 20 L gas fryer. 10 frying trials were carried out using Treatment Briquettes A and 10 frying trials were carried out using Treatment Briquettes B. Treatment Briquettes A were made according to the specification set out above save that they were dried at 130° C. for 6 hours whereas Treatment Briquettes B were made in the same way but were dried at 230° C. for 24 hours. Each frying trial comprised frying 10 lots of 900 gms of frozen pre-fried chips per day for five consecutive days: i.e. 45 kilograms of chips were cooked during each of the 40 frying trial.

Effect on Foaming

[0089] The results are tabulated below in tables 5 & 6.

TABLE-US-00006 TABLE 5 Treatment Briquettes A % of % of establishments establishments Energy Non- with this with this source Foaming foaming energy source energy source for fryer trials trials which don't foam which foam Electricity 2 8 80% 20% Gas 4 6 60% 40% Total 6 14  70% 30%

TABLE-US-00007 TABLE 6 Treatment Briquettes B % of % of establishments establishments Energy Non- with this with this source Foaming foaming energy source energy source for fryer trials trials which don't foam which foam Electricity 0 10 100% 0% Gas 0 10 100% 0% Total 0 20 100% 0%

[0090] It will be noted that with Treatment Briquettes B there was not a single instance of foaming in either the electric or the gas fryer. It will be observed that with Treatment Briquettes A the overall foaming rate was 30% whereas with treatment briquettes B the overall foaming rate was 0%. Thus it can be seen that the elevated temperature drying for a longer period of time completely eradicated foaming, even in the gas fryer.

Purification Performance of the Treatment Briquettes

[0091] Oils develop acidity during frying due to oxidation, hydrolysis and other decomposition routes. Different oils have different oxidation and hydrolysis rates. The free fatty acid level in any given oil in a fryer is determined by the starting FFA level, the subsequent rate of FFA generation and the amount of its elimination by distillation and absorption by food. It is essential therefore if meaningful data on FFA levels are to be obtained to use the same oil throughout all experiments. The trials described herein were all conducted with vegetable oil from the same manufacturer's (KTC) batch, which contains E900—a PDMS anti-foaming agent.

[0092] Two sets of trial frying runs were undertaken: one set with Treatment Briquettes A and one set with Treatment Briquettes B. An electric fryer was used for these frying trials. 10 lots of 900 gms of frozen pre-fried chips were fried each day for five days. At the end of each day a sample of the oil was collected. The samples were flushed with nitrogen and kept at minus 20° C. away from any source of light until analysed so as to prevent further breakdown of the oil.

[0093] The free fatty acid was measured for each sample using a titration procedure (AOCS method Ca 5a-40, IUPAC 2.201, AOAC 940.28 and see IUPAC (1979), Standard Methods for Oils, Fats and Derivatives, 6.sup.th edn, Pergamon Press, Oxford, reference 2) and the averaged results (expressed as percentages) are tabulated below:—

TABLE-US-00008 FFA % treatment FFA % treatment Day briquettes A briquettes B 0 0.04 0.04 1 0.32 0.34 2 0.37 0.38 3 0.37 0.39 4 0.41 0.43

[0094] Thus it can be seen that the use of Treatment Briquettes B gave a performance in terms of ffa reduction which was substantially identical to that obtained from the standard filter, which had been dried at 130 degrees for only 6 hours.

Total Polar Compounds

[0095] Some authors and experts in the field have questioned how reliable free fatty acid concentration is as a measure of oil quality, (see for example effective Process Control in Frying by GB Quaglia et al at page 237 of Frying, Improving quality, edited by J. B. Rossell, Woodhead Publishing Limited). Accordingly the amount of total polar compounds was also measured as it is (along with acid value) a very commonly used indicator of oil quality and is widely used in many international regulations: (see for example Fritch, C. W. 1981. Measurements of frying fat deterioration. A brief review. J. Am. Oil Chem Coc. 58: 272-274 and Firestone, D. 2007. Regulation of frying fat and oil, In “Deep Frying: Chemistry, Nutrition, and Practical Applications”. 2.sup.nd ed. Pp. 373-385. Erickson, M. D. ed. AOCS Press, Urbaba, USA.)

[0096] The content of total polar compounds in oil can be determined by the use of the methods set out in AOCS Cd_20-91 and ISO 8420. Typically a glass column (for example 35 cm in length and 2.1 cm in diameter) is used to effect the chromatography. A suitable eluent is a mixture of petroleum and diehthyl ether in the ration of 87:13 (v/v). The oil sample to be tested (2.5 g) is loaded into the packed column and the non-polar compounds (%) is calculated as the mass fraction of the total polar compounds in the oil sample as a percentage.

[0097] However the AOCS Cd_20-91 and ISO 8420 procedures need to be carried out in a laboratory with proper equipment by a skilled technician and is not suitable for on site testing. Accordingly we used a Testo 270 Deep frying oil tester (Testo Inc. Germany), which gives a more or less instantaneous reading of total polar compounds as a percentage when its probe is put into the oil to be tested and used in accordance with the manufacturer's instructions. The oil to be tested was tested at 55° C.

[0098] The oil samples collected for the previously referred to FFA testing (see above) were analysed using the Testo 270 and the results are tabulated below:—

TABLE-US-00009 TPC % Treatment TPC % Treatment Day Briquettes A Briquettes B 0 5.0 5.2 1 7.7 8.4 2 9.6 10.5 3 11.4 11.2 4 15.0 16.8

[0099] Thus it can be seen that the total polar compound concentration was comparable as between the oil treated with Treatment Briquette A (130° C./6 hours) and the oil treated with Treatment Briquette B (230° C./24 hours).

Aldehydes

[0100] The aldehyde concentration of the oil was also ascertained as described below. Aldehydes are a good indicator of oil quality for several reasons. Firstly aldehydes, even in very low concentrations, are known to cause many of the off-flavours observed in used cooking oils and in food fried in such cooking oils. Secondly such aldehydes are secondary oxidation products, resulting from the breakdown of primary oxidation products and therefore can be seen as a good proxy for the concentration of such primary oxidation products.

[0101] Thirdly many aldehydes are considered to be injurious to human health, (see for example Warning: thermally-stressed polyunsaturates are damaging to health, Martin Grootveld, Christopher J. L. Silwood and Andrew W. D. Claxson Food Chemistry 67 (1999) 211-213). During frying, polyunsaturated fatty acids oxidize and form degradation products with proven toxicity, such as 4-hydroxy-2-(E)-nonenal: (see for example Seppanen C M, Csallany A S (2001) Simultaneous Determination of Lipophilic Aldehydes by High-Performance Liquid Chromatography in Vegetable Oil. J Am Oil).

[0102] Particular aldehydes of interest include:—

(a) trans-2-alkenals
(b) trans,trans-alka-2,4-dienals,
(c) 4,5-epoxy-trans-2-alkenals
(d) 4-hydroxy-trans-2-alkenals
(e) cis,trans-alka-2,4-dienals and
(f) n-alkanals.

[0103] Oil samples collected from the previous FFA testing were analysed and detection and measurement of the concentrations of such aldehydes was determined in accordance with the methodology as set out on pages 22 to 23 of WO 2008/015481 A2, which is incorporated by reference herein and the results are tabulated below as between (a) the oil exposed to Treatment Briquettes A and (b) the oil exposed to Treatment Briquette B. 50 gm samples of the oil were taken, after the oil had cooled and been filtered using the fryers own internal particulate filter. The samples were then flushed with nitrogen and kept at minus 20° C. away from any source of light until analysed so as to prevent further breakdown of the oil. The results are tabulated below:—

TABLE-US-00010 4,5- trans- trans,trans- epoxy- 4-OH- cis,trans- n- 2- alka-2,4- trans-2- trans-2- alka-2,4- alka- 4 Days Alkenal dienal alkenal alkenal dienal nal Treat- 8.8 22.4 7.0 2.5 2.0 3.3 ment bri- quettes A Treat- 10.8 24.2 2.3 1.6 2.7 3.1 ment bri- quettes B

[0104] All units are mmol/kg oil detected in .sup.1HMR experiments conducted on sunflower oil.

[0105] Again the results as between the oil treated with Treatment Briquette A and Treatment Briquette B were broadly comparable, showing that elevated drying did not affect the performance of the filters.

Reduced Usage of Anti-Foaming Agent

[0106] The use of the invention described herein enables a reduced amount of anti-foaming agent to be used. A very commonly used anti-foaming agent used in cooking oil is PDMS—polydimethylsiloxane. According to the World Health Organization, the acceptable daily intake of PDMS is up to 1.5 mg/kg of body weight (INCHEM International Program on Chemical Safety, http://www.inchem.org/documents/jecfa/jeceval/jec_1943. htm) and the maximum allowed in foods by the FDA is 10 ppm (Food and Drug Administration, 21 CFR Part 173.340 Secondary Direct Food Additives Permitted in Food for Human Consumption. Defoaming Agents, http://www.accessdatalda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?fr=173.340). The amount of PDMS absorbed in fried potato chips increased exponentially with increasing PDMS contents in the frying oil (Freeman I P, Padley F B, Sheppard W L (1973) Use of Silicones in Frying Oils. J Am Oil Chem Soc 50:101-103). It is therefore advantageous to reduce the amount of PDMS used in cooking oil as much as possible. PDMS is typically used in frying oils in concentrations of ˜5 ppm in the oil.

[0107] Twenty sets of trial frying runs were undertaken: one set with Treatment Briquette A and one set with Treatment Briquette B. A 20 L gas fryer was used for these frying trials, with two filters used per fryer. For each set of trials, 10 lots of 900 gms of frozen pre-fried chips were fried each day for five days. The oil used was rapeseed oil which contained 5 ppm of PDMS for one series of frying runs and 10 ppm of PDMS for the other set of frying runs.

TABLE-US-00011 Rapeseed oil with Rapeseed oil with 5 ppm PDMS 15 ppm PDMS Treatment 2/5 0/5 Briquettes A Treatment 0/5 0/5 Briquettes B

[0108] It can be seen that with Treatment Briquettes A at a standard concentration of 5 ppm PDMS, two of five of the frying runs experienced foaming whereas at 15 ppm PDMS there were no instances of foaming. With Treatment Briquettes B there was no foaming in any of the five trials even at the standard PDMS dosage of 5 ppm. Thus it can be seen that the use of the filters made in accordance with the inventions herein disclosed enables a reduction in the amount of PDMS required to successfully and consistently suppress foaming.