Patent Application
20080026104
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art (e.g. in chilled confectionery/frozen confectionery manufacture, and chemistry). Definitions and descriptions of various terms and techniques used in chilled/frozen confectionery manufacture are found in Ice Cream, 4th Edition, Arbuckle (1986), Van Nostrand Reinhold Company, New York, N.Y.
The present invention will now be further described with reference to the following examples, which are illustrative only and non-limiting.
Materials and Methods
Process Conditions
Mix Manufacture:
In a jacketed 500 litre mix tank, water is added at 85° C., then milk ingredients, sugar, stabilizers, emulsifier, fat are added and mixed with high shear mixer. The premix is heated with a plate heat exchanger to 83° C. and homogenized with a Crepaco single stage valve homogeniser at either 150 or 300 bar. After holding at 83° C. for 15 seconds the mix is cooled with a plate heat exchanger to 5° C. The mix was held at this temperature for at least two hours prior to freezing. Immediately prior to freezing, the probiotic culture (supplied as either freeze dried or DVS (direct vat set) frozen pellets) was then added and mixed well.
Freezing Process:
The aged mix was processed through an ice cream freezer (Crepaco W04 freezer with a series 30 dasher operating at 4 bar barrel pressure). Ice cream was produced at a mix throughput of 200 l/hr at 100% overrun with an extrusion temperature of −7.0° C. The outlet of the freezer was connected to a single screw extruder (SSE) (as described in WO98/09534) and operated at an inlet pressure of 7 bar and at a range of torque set points from 600 Nm to 1250 Nm.
Calculation of shear stress and viscosity of the ice cream within a screw channel are based on the assumption that the system is, or can be described as, wide gap concentric cylinders of the screw body inside the barrel
Shear stress=τ=Md/2Br2L where:
Shear rate=2Σ/n(1−b2/n) where
Standard Storage
Samples taken directly from the blast freezer after 2 hrs and placed in the −25° C. cold store for the 24 week storage time. Viability of initial mix, freshly produced and stored ice cream shown below, expressed as absolute count (cfu/g) and % loss compared to unfrozen mix.
Sample Preparation for LTSEM:
The microstructure of ice cream samples was visualized by Low Temperature Scanning Electron Microscopy (LTSEM). All samples were stored at −80° C. prior to structural analysis. The samples were prepared using the Oxford instruments CT1500HF preparation equipment attached to the microscope. A sample at −80° C. of size 5×5×10 mm was taken from the ice cream block. This sample was mounted onto an aluminium stub using a Tissue Tek: OCT™ compound (PVA 11%, Carbowax 5% and 85% non-reactive components) on the point of freezing.
The sample including the holder was plunged into liquid nitrogen slush and transferred to a low temperature preparation chamber: Oxford: Instrument CT1500HF. The chamber is under vacuum, approximately 10−4 bar, and the sample is warmed up to −90° C. Ice is slowly etched to reveal surface details not caused by the ice itself, so water is removed at this temperature under constant vacuum for 60 to 90 seconds. Once etched, the sample is cooled to −110° C. ending up the sublimation, and coated with gold using argon plasma. This process also takes place under vacuum with an applied pressure of 10−1 millibars and current of 6 milliamps for 45 seconds. The sample is then transferred to a conventional Scanning Electron Microscope (JSM 5600), fitted with an Oxford Instruments cold stage at a temperature of −160° C. The sample is examined and areas of interest captured via digital image acquisition software.
Gas Cell and Ice Crystal Sizing Method
The gas structure in ice cream was quantified by measuring the gas cell size distribution from SEM micrographs using the AnalySIS 2.11—package AUTO (SIS Munster, Germany) with ‘B’ version software. The AnalySIS programme was run using digital data direct from the JSM 5600 microscope. The optimum magnification was such that there were less than 300 gas cells per image. The programme was used manually by drawing around particle boundaries. The distribution was analysed using the maximum diameter parameter. All gas cells present on an SEM micrograph were counted and up to six SEM images were used. Generally, at least 300 gas cells were counted. The average size was determined as the number average, d(1,0), of the individual cell sizes. Ice crystals were also sized from SEM micrographs in a similar manner.
Prior to freezing, the probiotic bacteria were added to each mix at +5° C. in the form of frozen pellets such that the starting concentration of bacteria was 1.0×108 per gram of mix in all cases.
Each mix containing the probiotic bacteria was processed through a Crepaco WO4 ice cream freezer and then through a single screw extruder (described in WO98/09534).
The Crepaco freezer was operated such that overrun ex-freezer was about 100% and the temperature at extrusion about −6° C. to −7° C. (typical for this type of formulation).
The single screw extruder was operated with three torque set points of 750 Nm, 1000 Nm & 1250 Nm (corresponding to a calculated shear stress of 21000, 28000 & 35000 Pa respectively). This resulted in extrusion temperatures after the screw extruder in the range −10° C. to −12° C.
Samples of the frozen aerated confection were taken immediately after passing through the Crepaco freezer and after passing through the Crepaco freezer followed by the single screw extruder.
The samples were stored at −25° C. for 24 weeks after which the levels of probiotic bacteria were measured.
The air cell sizes and ice crystal sizes were measured, as described above on selected samples after a minimum storage time of 24 weeks at −25° C.
Results and Discussion
Table 1 gives the recipes used to exemplify the invention. Recipe 1 is a typical low fat ice cream formulation containing 4% fat and 10% MSNF.
Recipes 2 and 3 are essentially the same but with some of the MSNF and water replaced by 25% and 50% yoghurt respectively.
Air Cell & Ice Crystal Sizes
Table 2 gives the measured mean air cell sizes and ice crystal sizes for the frozen aerated confections produced using Recipe 1.
These results show that the mean air cell and mean ice crystal sizes are much smaller when processed through the combination of Crepaco freezer and the single screw extruder compared with the Crepaco freezer alone.
The values for the mean air cell size and mean ice crystal size of 93 micron and 55 micron respectively are typical for a low fat formulation of this type when processed through a Crepaco freezer operating under standard conditions.
The additional processing step of single screw extrusion significantly reduces the mean air cell size and the mean ice crystal size.
The values for these parameters at the lowest torque setting used (750 Nm) were mean air cell size 31 micron and mean ice crystal size 45 micron.
An informal taste panel considered the low torque SSE sample to be significantly thicker, creamier and less cold eating than the equivalent sample processed using the Crepaco freezer alone.
Conclusion
Low torque SSE processing produces an aerated frozen confection with significantly smaller air cells and ice crystals compared to the equivalent product processed through a standard ice cream freezer alone.
This finer microstructure results in a product that is thicker, creamier and less cold eating than a conventionally frozen low fat product.
Probiotic Viability
Table 3 gives the levels of probiotic bacteria measured after 24 weeks storage at −25° C. compared with the initial starting concentrations of 1.0×108 per gram of mix.
The data are given for the three recipes used and for four different processing regimes.
(1) Crepaco freezer alone
(2) Crepaco freezer followed by SSE operating at torque set point 750 Nm
(3) Crepaco freezer followed by SSE operating at torque set point 1000 Nm
(4) Crepaco freezer followed by SSE operating at torque set point 1250 Nm
In all cases the probiotic bacteria levels were lower in the stored frozen samples compared to the equivalent fresh mix. The figures in parentheses give the % losses after frozen storage relative to the starting concentration in the mix.
It is seen that there are no systematic trends in losses with increasing yoghurt levels in the mix. In contrast however, there are systematic trends as a consequence of the method of processing.
The lowest losses occur when the Crepaco freezer alone is used. However, such a product also has the lowest product quality, as determined by air cell and ice crystal size and sensory panel. Losses increase when processed through the single screw extruder. In general, as the torque set point is increased the level of losses also increases. Nonetheless, if the shear stress exerted by the SSE is limited to no more than 25000 Pa, then losses can be kept below one third, which is acceptable, whilst retaining good product microstructure.
Conclusion
SSE can be used to produce a low fat probiotic ice cream having both good product microstructure (and therefore quality to the consumer) whilst also having good levels of probiotic bacteria. However, to keep probiotic losses to an acceptable level during the freezing process (e.g. under one third) the maximum shear stress exerted by the SSE should be limited to no more than around 25000 Pa.
The various features and embodiments of the present invention, referred to in individual sections above apply, as appropriate, to other sections, mutatis mutandis. Consequently features specified in one section may be combined with features specified in other sections, as appropriate.
All publications mentioned in the above specification are herein incorporated by reference. Various modifications and variations of the described methods and products of the invention will be apparent to those skilled in the art without departing from the scope of the invention. Although the invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. Indeed, various modifications of the described modes for carrying out the invention which are apparent to those skilled in the relevant fields are intended to be within the scope of the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| EP06117998 | Jul 2006 | EP | regional |
